SMTP stress

[#1]

There must be  a simple answer but it's got me beaten!

I've just got a new MacBook, and I've set up Mac mail by copying settings from my old one. Incoming mails arrive fine, but I can't send any out. The Mail Preferences page insists that the server is offline and can't be contacted. I've rechecked the SMTP settings many times, but trying to change anything brings up the 'Can't connect to server' message.

What am I doing wrong?

Alex.

[#2]

Which email client and settings are you using for smtp?

They should be

SMTP: relay.plus.net port 587 encryption STARTTLS <-- preferred setting
or
SMTP: relay.plus.net port 465 encryption SSL 

[#3]

Mac Mail.

Turning on TLS on port 587 has got it working, but the odd thing (to me anyway) is that my old Mac sends perfectly well without TLS.

Thanks for your help!

Alex.

[#4]

There is every possibility that the later version of the email client on your new MAC is refusing to use an unencrypted connection.

It can also be confusing that different clients will use explicit SSL, SSL/TLS, STARTTLS options or infer any of them from one of them.  For example port 587 does not work with SSL or SSL/TLS but does work with STARTTLE - some clients do not offer the STARTTLS option, either explicitly or by implication.

For example iPhones offer "Use SSL" and selecting that configures STARTTLS on the SMTP server connection.