I am using eM Client version 7.1.34849.0 which I believe is the latest version.
If I send an email to an incorrectly structured email address such as below : 
It has a full stop - or period - after the com
The email isn’t sent and errors with the following:
However the email is not shown in the Outbox.
If you do a refresh you get the same “An error has occurred” as above and if you close eM Client you get this message:
It doesn’t matter if you say "Yes " or “No”, it doesn’t help the problem. Re-opening the program just brings up the “An error has occurred” and the loop starts again.
If I was able to see the email in the Outbox, I could obviously delete it and all would be good.
This has occurred on a Hotmail account and a Office365 email with a custom domain name. I haven’t tried it with another type of email so I am not sure if this is a Microsoft Exchange issue with eM Client as both systems now use Exchange or whether it is just a general error.
The email is not shown in the Outbox on the Hotmail/Office365 Webmail either.
I will test with a gmail account but if anybody ha any ideas or workarounds, I would be very grateful.
And here is the log:
19:30:14 Online state: changed to online due to NetworkAvailability
19:30:14 [email protected] [Offline Address Book] Synchronizing folder list
19:30:15 [email protected] [Exchange Web Services] Sending email
19:30:15 [email protected] [Exchange Web Services] Sending email
19:30:15 MailClient.Storage.Application.OperationException: Sending email failed due to the following error: At least one recipient isn’t valid., Recipient “[email protected].” isn’t resolved. All recipients must be resolved before a message can be submitted. —> Microsoft.Exchange.WebServices.Data.ServiceResponseException: At least one recipient isn’t valid., Recipient “[email protected].” isn’t resolved. All recipients must be resolved before a message can be submitted.
19:30:15 at Microsoft.Exchange.WebServices.Data.ServiceResponse.InternalThrowIfNecessary()
19:30:15 at Microsoft.Exchange.WebServices.Data.MultiResponseServiceRequest1.Execute() 19:30:15 at Microsoft.Exchange.WebServices.Data.ExchangeService.InternalCreateItems(IEnumerable1 items, FolderId parentFolderId, Nullable1 messageDisposition, Nullable1 sendInvitationsMode, ServiceErrorHandling errorHandling)
19:30:15 at Microsoft.Exchange.WebServices.Data.ExchangeService.CreateItem(Item item, FolderId parentFolderId, Nullable1 messageDisposition, Nullable1 sendInvitationsMode)
19:30:15 at Microsoft.Exchange.WebServices.Data.Item.InternalCreate(FolderId parentFolderId, Nullable1 messageDisposition, Nullable1 sendInvitationsMode)
19:30:15 at Microsoft.Exchange.WebServices.Data.EmailMessage.InternalSend(FolderId parentFolderId, MessageDisposition messageDisposition)
19:30:15 at MailClient.Protocols.Exchange.ExchangeMailSynchronizer.<>c__DisplayClass18_0.b__0(WorkerStatus status, CancellationToken cancellationToken)
19:30:15 at MailClient.Protocols.Exchange.ExchangeGenericCommand.Execute(WorkerStatus status)
19:30:15 — End of inner exception stack trace —
19:30:15 at MailClient.Protocols.Exchange.ExchangeGenericCommand.Execute(WorkerStatus status)
19:30:15 at MailClient.Commands.Command.Process(WorkerStatus status)
19:30:15 [email protected] [Offline Address Book] Synchronizing folder list
19:30:15 [email protected] [Offline Address Book] Synchronizing folder list
19:30:15 [email protected] [Offline Address Book] Synchronizing folder '[email protected]/Offline Global Address List/'
19:30:15 [email protected] [Offline Address Book] Synchronizing folder '[email protected]/Offline Global Address List/'
Many thanks in advance for any help.