Mail app keeps trying to connect even though set to work offline
I have wireless internet access via my work but my employer (in their wisdom) had blocked access to the mail ports. I can browse the internet OK but can neither send nor receive emails. This doesn't bother me but I do sometimes like to work offline on emails which I will send later.
Using the Mail.app, I set the Mailbox > Online status for all my accounts to 'Work offline'. Despite this, I am plagued with pop-up dialogues saying 'The operation couldn’t be completed. Connection refused'. These are tedious and annoying and, since I specifically want to work offline, I don't know why a connection is being requested.
Is there anything I can do to stop this behaviour? [Yes, I could use the web interface - which is not blocked, but I much prefer the mail.app].