SMTP EHLO when no IPv6 on client

Initial setup
1

I am unable to connect to an Exchange Server 2003 (yes its old) because the EHLO greeting is generating an IPv6 pass-through address like:

EHLO [IPv6:::ffff:172.16.4.86] instead of EHLO [172.16.4.86]

The computer eM is running on is running Windows 10 with IPv6 disabled. eM should send the latter format, Exchange Server 2003 can’t handle this format. Here is the SMTP log file from eM:

15:58:19.135|001| eM Client 10.4.5326+97a2e75a43 (Windows)
15:58:19.135|001| Account’s UID is 7ebadcc0-5ecb-481b-9953-5ee2889b5da0
15:58:19.135|001| AccountBase.ChangeOnlineState : State changed to ONLINE due User
15:58:19.152|023| SMTP S: 220 pilgrim.com Microsoft ESMTP MAIL Service, Version: 6.0.3790.4675 ready at Fri, 12 Jun 2026 15:58:19 -0400
15:58:19.152|023| SMTP C: EHLO [IPv6:::ffff:172.16.4.86]
15:58:24.166|023| SMTP S: 501 5.5.4 Invalid Address
15:58:24.166|023| SMTP C: LHLO [IPv6:::ffff:172.16.4.86]
15:58:29.184|023| SMTP S: 500 5.3.3 Unrecognized command
15:58:29.184|023| SMTP C: HELO [IPv6:::ffff:172.16.4.86]
15:58:34.201|023| SMTP S: 501 5.5.4 Invalid Address
15:58:34.205|023| Exception: MailClient.Storage.Application.OperationException: SMTP server didn’t like our greetings and replied with: 5.5.4 Invalid Address
15:58:34.205|023|
15:58:34.205|023| at MailClient.Protocols.Smtp.SmtpSendCommand.SendGreetings()
15:58:34.205|023| at MailClient.Protocols.Smtp.SmtpSendCommand.Connect(WorkerStatus status)
15:58:34.205|023| at MailClient.Protocols.Smtp.SmtpSendCommand.Execute(WorkerStatus status)
15:58:34.205|023| at MailClient.Commands.Command.Process(WorkerStatus status)
15:58:34.205|023| AccountBase.GoOfflineAsync : State changed to OFFLINE due BrokenConnection
15:58:34.205|01F| AccountBase.ChangeOnlineState : State changed to OFFLINE due BrokenConnection

2

If you are running eM Client V9 or V10, your old 2003 exchange server might not be supported anymore. It’s not likely anyone on this free user forum would be able to help you with that.

Suggest you contact Official Support via going to the following VIP support page and login and lodge a support ticket and link this thread.

If you have run out of your 12 months support time you can get another year support extension via the following page VIP Support Extension | eM Client

3

Thanks. I’ll log an official support issue, which is what I should have done in the first place. Our domain is now hosted so it isn’t really an issue for me.