SMTP ports on desktop and mobile

Question

For years I used port 465 for my outgoing email with no problem, but suddenly my desktop client (eM Client) refused to send messages. I went to my provider for advice and they claim they haven't changed any settings and it's my client's fault. Hmm... I've changed the port to 587 and it works smoothly now.

But I've noticed that my mobile client (AirMail on iOS) still uses port 465! What's more, when I tried updating it to 587, it stopped working and I had to revert to 465.

So now I have working mail on desktop on port 587 and on mobile on port 465, all with the same provider! It's no real issue, but I can help wondering: what's the real reason for it? Can it be actually attributed to the client software I use?

Answer 1

It would be much easier to provide useful answers if you could provide more details, such as what error responses your clients got from the server when they tried to send email, and what you tried to do to fix the problem.

This is a bit of a wild guess: maybe your desktop is no longer able to send email over a secure (TLS) connection on port 465, but it can send email over an insecure connection on port 587. That might indicate a problem with a certificate.

Answer 2

Indeed! Here's the error message I was getting:

[CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS MULTIAPPEND UNSELECT IDLE CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS ACL RIGHTS=texk QUOTA STARTTLS AUTH=PLAIN AUTH = LOGIN] Dovecot ready.'.

I may be wrong as I have no access to my desktop at the moment but I believe that sending over 587 happens with SSL, at least that's the security set in the account configuration.