I was testing Stalwart using Outlook (my clients use Windows :( )

[lulu-2021]

In order to setup a new Mail profile/account in Outlook (Windows 10) - an test email is sent and this fails. (its hard to determine exactly what outlook does) Since a few years how this "test" is enforced on the client setup and if it fails the client/account setup process can't saved. I am currently using Thunderbird on Linux & OSX without any issues - so am wondering why Outlook would have a problem authenticating with Stalwart (tried 465/SSL and 587/TLS - and both have this issue - any ideas why this may be ?

[mdecimus]

I don't have a Windows computer nearby to help you, but I believe that Outlook tries to discover the IMAP/SMTP server details automatically and this fails. Try selecting the option to manually set up the account and use ports 143 for IMAP (or 993 for IMAP TLS) and 465 for SMTP submissions.