Mail fail - smtp won't send, connection doctor says fine.

Question

Hi Guys,
I've been searching around t'interweb and I can't see to find a fix for this. Mac mail has always been really solid for me, but in the past couple of months mine has gone wonky. First it stopped searching, which again despite trying various things I found and re-installing the whole system, I could not fix.
Now, and more disastrously it has stopped allowing me to send emails through the SMTP server.
It throws up a dialog box saying could not send through this server, try another.
I contacted my exchange mail provider, have gone through settings, and they all seem fine. They've tested it all from their end too. They even issued me an alternate SMTP server and that doesn't work either. Argh. When I run connection doctor it can log in fine. But when I send mail it gets stuck.
Any thoughts its seriously messing up my day/evening/life at the moment.
Help much appreciated.

Answer 1

The typical problem when the SMTP requires no separate authentication, is that it must use Port 25, but more and more connection providers are blocking Port 25, as it is the least secure again misuse. For those venues where Port 25 use is still permitted, you often must be approved to use it by the IP address of the modem. You have said this problem is present when you are at more than one venue and mention the use of a dongle. Has the modem at any venue changed, and might some ISPs involved have recently acted to block Port 25?
You should investigate whether your Exchange provider can offer you a fully authenticated SMTP that will allow you to use either Port 587 or Port 465.
Ernie