SMTP server doesn’t support authentication

trvbrown · November 15, 2025, 12:16am

Once recently and now again I am unable to send emails via my default server, receiving the above error message. I am running V10

cyberzork · November 15, 2025, 12:25am

SMTP server doesn’t support authentication

If this is a POP or IMAP account where you manually specify a username and password for your SMTP server, go to “Menu / Accounts” and click on your account SMTP tab and set it to “Use Identity Credentials” if it’s not already.

trvbrown · November 15, 2025, 12:33am

Port 587 (POP), Don’t use secure connection, server requires authentication, use identity credentials

cyberzork · November 15, 2025, 12:40am

Port 587 (POP), Don’t use secure connection

If you don’t want to use a secure connection to send mail, then you would normally set a POP SMTP Port to 25 with Use SSL/TLS if available.

But normally you would use SMTP Port 587 with Force usage of SSL/TLS or alt Port 465

Port 587 = Force usage of SSL/TLS
Port 465 = Use SSL/TLS on special port (legacy)
Port 25 = Use SSL/TLS if available

trvbrown · November 15, 2025, 12:50am

None of those settings work, these settings have been used for years with eM Client without problems

trvbrown · November 15, 2025, 1:10am

On my android phone when sending: cannot connect to server

cyberzork · November 15, 2025, 1:30am

None of those settings work, these settings have been used for years with eM Client without problems

If none of those SMTP port settings work then either you have a current SMTP server issue or you have something locally blocking those SMTP ports.

Sometimes ports can be blocked by eg: optionally installed firewall security programs or optionally installed antivirus programs or vpns. So if you have anything like that installed “other than what comes default with your OS”, then try completely disabling those to test.

If you have nothing like that optionally installed or you do but disabling made no difference, then must be some either “external SMTP server issue” or “a physical internet connection issue”.

So I would next “power off your computer and modem for say 2 mins” and then turn back on and then see if you can send mail with the same SMTP settings as you had previously.

If you still carn’t, “click the dropdown on the right of Refresh top left” and click “Show Operations” and click the “Log tab” and look for any obvious error messages and paste them in this thread and we might then see what’s wrong blank out anything personal in the log errors.

trvbrown · November 15, 2025, 1:38am

Thank you, I will see what I can do

trvbrown · November 15, 2025, 1:44am

eM Client 10.3.2619+1e54f4a61e (Windows)
2:14:19 pm Online state: changed to online due to NetworkAvailability
2:14:19 pm trvbrown SMTP Connecting: To trvbrown
2:14:19 pm [email protected] POP3 Connecting: To [email protected]
2:14:19 pm trvbrown POP3 Connecting: To trvbrown
2:14:19 pm [email protected] IMAP Synchronizing folder ‘/All Mail’
2:14:19 pm trvbrown [SMTP] MailClient.Storage.Application.OperationException: SMTP server doesn’t support authentication.
at MailClient.Protocols.Smtp.SmtpSendCommand.Authenticate(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Connect(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Execute(WorkerStatus status)
at MailClient.Commands.Command.Process(WorkerStatus status)
AccountId = null
AccountName = null
RunInPlace = False
GUIStatus_Exception_Reported = True
2:14:19 pm trvbrown POP3 Connected: To trvbrown
2:14:19 pm trvbrown POP3 Listing messages: From trvbrown
2:14:19 pm [email protected] Google Contacts Synchronizing folder list
2:14:19 pm [email protected] Google Contacts Synchronizing folder ‘/Other Contacts’
2:14:19 pm trvbrown POP3 Disconnected: From trvbrown
2:14:19 pm trvbrown POP3 Disconnected: Done
2:14:20 pm [email protected] POP3 Connected: To [email protected]
2:14:20 pm [email protected] POP3 Listing messages: From [email protected]
2:14:20 pm [email protected] POP3 Disconnected: From [email protected]
2:14:20 pm [email protected] POP3 Disconnected: Done
2:14:24 pm [email protected] IMAP Synchronizing folder list
2:14:25 pm [email protected] IMAP Synchronizing folder ‘/All Mail’
2:14:26 pm [email protected] IMAP Synchronizing folder ‘/Junk Email’
2:14:30 pm [email protected] IMAP Synchronizing folder ‘/Trash’
2:24:19 pm trvbrown SMTP Connecting: To trvbrown
2:24:19 pm trvbrown POP3 Connecting: To trvbrown
2:24:19 pm [email protected] POP3 Connecting: To [email protected]
2:24:19 pm [email protected] Google Contacts Synchronizing folder ‘/Other Contacts’
2:24:19 pm [email protected] IMAP Synchronizing folder ‘/All Mail’
2:24:19 pm trvbrown [SMTP] MailClient.Storage.Application.OperationException: SMTP server doesn’t support authentication.
at MailClient.Protocols.Smtp.SmtpSendCommand.Authenticate(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Connect(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Execute(WorkerStatus status)
at MailClient.Commands.Command.Process(WorkerStatus status)
AccountId = null
AccountName = null
RunInPlace = False
GUIStatus_Exception_Reported = True
2:24:19 pm [email protected] POP3 Connected: To [email protected]
2:24:19 pm [email protected] POP3 Listing messages: From [email protected]
2:24:19 pm [email protected] POP3 Disconnected: From [email protected]
2:24:19 pm [email protected] POP3 Disconnected: Done
2:24:19 pm trvbrown POP3 Connected: To trvbrown
2:24:19 pm trvbrown POP3 Listing messages: From trvbrown
2:24:19 pm trvbrown POP3 Disconnected: From trvbrown
2:24:19 pm trvbrown POP3 Disconnected: Done
2:24:20 pm [email protected] IMAP Synchronizing folder list
2:24:21 pm [email protected] IMAP Synchronizing folder ‘/All Mail’
2:24:22 pm [email protected] IMAP Synchronizing folder ‘/Junk Email’
2:24:23 pm [email protected] IMAP Synchronizing folder ‘/Trash’
2:34:19 pm trvbrown SMTP Connecting: To trvbrown
2:34:19 pm trvbrown POP3 Connecting: To trvbrown
2:34:19 pm [email protected] POP3 Connecting: To [email protected]
2:34:19 pm [email protected] Google Contacts Synchronizing folder ‘/Other Contacts’
2:34:19 pm [email protected] IMAP Synchronizing folder ‘/All Mail’
2:34:19 pm trvbrown [SMTP] MailClient.Storage.Application.OperationException: SMTP server doesn’t support authentication.
at MailClient.Protocols.Smtp.SmtpSendCommand.Authenticate(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Connect(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Execute(WorkerStatus status)
at MailClient.Commands.Command.Process(WorkerStatus status)
AccountId = null
AccountName = null
RunInPlace = False
GUIStatus_Exception_Reported = True
2:34:19 pm trvbrown POP3 Connected: To trvbrown
2:34:19 pm trvbrown POP3 Listing messages: From trvbrown
2:34:19 pm [email protected] POP3 Connected: To [email protected]
2:34:19 pm [email protected] POP3 Listing messages: From [email protected]
2:34:19 pm trvbrown POP3 Disconnected: From trvbrown
2:34:19 pm trvbrown POP3 Disconnected: Done
2:34:19 pm [email protected] POP3 Disconnected: From [email protected]
2:34:19 pm [email protected] POP3 Disconnected: Done
2:34:20 pm [email protected] IMAP Synchronizing folder list
2:34:21 pm [email protected] IMAP Synchronizing folder ‘/All Mail’
2:34:22 pm [email protected] IMAP Synchronizing folder ‘/Junk Email’
2:34:25 pm [email protected] IMAP Synchronizing folder ‘/Trash’
2:39:37 pm trvbrown SMTP Connecting: To trvbrown
2:39:37 pm trvbrown POP3 Connecting: To trvbrown
2:39:38 pm trvbrown [SMTP] MailClient.Storage.Application.OperationException: SMTP server doesn’t support authentication.
at MailClient.Protocols.Smtp.SmtpSendCommand.Authenticate(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Connect(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Execute(WorkerStatus status)
at MailClient.Commands.Command.Process(WorkerStatus status)
AccountId = null
AccountName = null
RunInPlace = False
GUIStatus_Exception_Reported = True
2:39:38 pm trvbrown POP3 Connected: To trvbrown
2:39:38 pm trvbrown POP3 Listing messages: From trvbrown
2:39:38 pm trvbrown POP3 Disconnected: From trvbrown
2:39:38 pm trvbrown POP3 Disconnected: Done

trvbrown · November 15, 2025, 1:44am

eM Client 10.3.2619+1e54f4a61e (Windows)
2:14:19 pm Online state: changed to online due to NetworkAvailability
2:14:19 pm trvbrown SMTP Connecting: To trvbrown
2:14:19 pm [email protected] POP3 Connecting: To [email protected]
2:14:19 pm trvbrown POP3 Connecting: To trvbrown
2:14:19 pm [email protected] IMAP Synchronizing folder ‘/All Mail’
2:14:19 pm trvbrown [SMTP] MailClient.Storage.Application.OperationException: SMTP server doesn’t support authentication.
at MailClient.Protocols.Smtp.SmtpSendCommand.Authenticate(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Connect(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Execute(WorkerStatus status)
at MailClient.Commands.Command.Process(WorkerStatus status)
AccountId = null
AccountName = null
RunInPlace = False
GUIStatus_Exception_Reported = True
2:14:19 pm trvbrown POP3 Connected: To trvbrown
2:14:19 pm trvbrown POP3 Listing messages: From trvbrown
2:14:19 pm [email protected] Google Contacts Synchronizing folder list
2:14:19 pm [email protected] Google Contacts Synchronizing folder ‘/Other Contacts’
2:14:19 pm trvbrown POP3 Disconnected: From trvbrown
2:14:19 pm trvbrown POP3 Disconnected: Done
2:14:20 pm [email protected] POP3 Connected: To [email protected]
2:14:20 pm [email protected] POP3 Listing messages: From [email protected]
2:14:20 pm [email protected] POP3 Disconnected: From [email protected]
2:14:20 pm [email protected] POP3 Disconnected: Done
2:14:24 pm [email protected] IMAP Synchronizing folder list
2:14:25 pm [email protected] IMAP Synchronizing folder ‘/All Mail’
2:14:26 pm [email protected] IMAP Synchronizing folder ‘/Junk Email’
2:14:30 pm [email protected] IMAP Synchronizing folder ‘/Trash’
2:24:19 pm trvbrown SMTP Connecting: To trvbrown
2:24:19 pm trvbrown POP3 Connecting: To trvbrown
2:24:19 pm [email protected] POP3 Connecting: To [email protected]
2:24:19 pm [email protected] Google Contacts Synchronizing folder ‘/Other Contacts’
2:24:19 pm [email protected] IMAP Synchronizing folder ‘/All Mail’
2:24:19 pm trvbrown [SMTP] MailClient.Storage.Application.OperationException: SMTP server doesn’t support authentication.
at MailClient.Protocols.Smtp.SmtpSendCommand.Authenticate(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Connect(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Execute(WorkerStatus status)
at MailClient.Commands.Command.Process(WorkerStatus status)
AccountId = null
AccountName = null
RunInPlace = False
GUIStatus_Exception_Reported = True
2:24:19 pm [email protected] POP3 Connected: To [email protected]
2:24:19 pm [email protected] POP3 Listing messages: From [email protected]
2:24:19 pm [email protected] POP3 Disconnected: From [email protected]
2:24:19 pm [email protected] POP3 Disconnected: Done
2:24:19 pm trvbrown POP3 Connected: To trvbrown
2:24:19 pm trvbrown POP3 Listing messages: From trvbrown
2:24:19 pm trvbrown POP3 Disconnected: From trvbrown
2:24:19 pm trvbrown POP3 Disconnected: Done
2:24:20 pm [email protected] IMAP Synchronizing folder list
2:24:21 pm [email protected] IMAP Synchronizing folder ‘/All Mail’
2:24:22 pm [email protected] IMAP Synchronizing folder ‘/Junk Email’
2:24:23 pm [email protected] IMAP Synchronizing folder ‘/Trash’
2:34:19 pm trvbrown SMTP Connecting: To trvbrown
2:34:19 pm trvbrown POP3 Connecting: To trvbrown
2:34:19 pm [email protected] POP3 Connecting: To [email protected]
2:34:19 pm [email protected] Google Contacts Synchronizing folder ‘/Other Contacts’
2:34:19 pm [email protected] IMAP Synchronizing folder ‘/All Mail’
2:34:19 pm trvbrown [SMTP] MailClient.Storage.Application.OperationException: SMTP server doesn’t support authentication.
at MailClient.Protocols.Smtp.SmtpSendCommand.Authenticate(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Connect(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Execute(WorkerStatus status)
at MailClient.Commands.Command.Process(WorkerStatus status)
AccountId = null
AccountName = null
RunInPlace = False
GUIStatus_Exception_Reported = True
2:34:19 pm trvbrown POP3 Connected: To trvbrown
2:34:19 pm trvbrown POP3 Listing messages: From trvbrown
2:34:19 pm [email protected] POP3 Connected: To [email protected]
2:34:19 pm [email protected] POP3 Listing messages: From [email protected]
2:34:19 pm trvbrown POP3 Disconnected: From trvbrown
2:34:19 pm trvbrown POP3 Disconnected: Done
2:34:19 pm [email protected] POP3 Disconnected: From [email protected]
2:34:19 pm [email protected] POP3 Disconnected: Done
2:34:20 pm [email protected] IMAP Synchronizing folder list
2:34:21 pm [email protected] IMAP Synchronizing folder ‘/All Mail’
2:34:22 pm [email protected] IMAP Synchronizing folder ‘/Junk Email’
2:34:25 pm [email protected] IMAP Synchronizing folder ‘/Trash’
2:39:37 pm trvbrown SMTP Connecting: To trvbrown
2:39:37 pm trvbrown POP3 Connecting: To trvbrown
2:39:38 pm trvbrown [SMTP] MailClient.Storage.Application.OperationException: SMTP server doesn’t support authentication.
at MailClient.Protocols.Smtp.SmtpSendCommand.Authenticate(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Connect(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Execute(WorkerStatus status)
at MailClient.Commands.Command.Process(WorkerStatus status)
AccountId = null
AccountName = null
RunInPlace = False
GUIStatus_Exception_Reported = True
2:39:38 pm trvbrown POP3 Connected: To trvbrown
2:39:38 pm trvbrown POP3 Listing messages: From trvbrown
2:39:38 pm trvbrown POP3 Disconnected: From trvbrown
2:39:38 pm trvbrown POP3 Disconnected: Done
2:42:51 pm [email protected] SMTP Connecting: To [email protected]
2:42:51 pm trvbrown SMTP Connecting: To trvbrown
2:42:52 pm trvbrown [SMTP] MailClient.Storage.Application.OperationException: SMTP server doesn’t support authentication.
at MailClient.Protocols.Smtp.SmtpSendCommand.Authenticate(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Connect(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Execute(WorkerStatus status)
at MailClient.Commands.Command.Process(WorkerStatus status)
— End of stack trace from previous location —
at MailClient.Accounts.AccountManager.SendAsync(IAccount account, CancellationToken cancellationToken)
at MailClient.Reminders.ReminderManager.TimerSendLaterTrigger(Object sender, ElapsedEventArgs e)
AccountId = null
AccountName = null
RunInPlace = False
GUIStatus_Exception_Reported = True
2:42:52 pm trvbrown [SMTP] MailClient.Storage.Application.OperationException: SMTP server doesn’t support authentication.
at MailClient.Protocols.Smtp.SmtpSendCommand.Authenticate(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Connect(WorkerStatus status)
at MailClient.Protocols.Smtp.SmtpSendCommand.Execute(WorkerStatus status)
at MailClient.Commands.Command.Process(WorkerStatus status)
— End of stack trace from previous location —
at MailClient.Accounts.AccountManager.SendAsync(IAccount account, CancellationToken cancellationToken)
AccountId = null
AccountName = null
RunInPlace = False
GUIStatus_Exception_Reported = True

cyberzork · November 15, 2025, 2:19am

From your logs “If you definitely have nothing optionally installed and running in the background like I mentioned above” and rebooting your modem and computer didn’t make any difference, then sounds like “an actual SMTP server issue” to me where something may have changed on the server end as far as their authentication sending mail etc or something possibly within your OS itself has changed causing it to not authenticate anymore.

So as you have Windows 10 or 11 or a recent Mac OS Sonoma, Sequoia, Tahoe, then I would first contact your SMTP server technical support and let them know what SMTP server settings and it just suddenly stopped and give them that specific “SMTP server doesn’t support authentication” error.

Failing that if they say their SMTP server end hasn’t changed then you will need official eM Client support. So if you have a current active paid Pro Personal or Business version, go to the VIP support page and login and lodge a support ticket for investigation and attach this thread URL.

trvbrown · November 15, 2025, 2:22am

Resetting the modem has fixed the issue, thanks very much for your patience, regards Trevor