Can't send using mail.com via outlook

I have read the threads covering this problem which seem to have come to a halt a couple of years ago and have tried all of the solutions offered.

I have set up a mail.com address which works fine from the internet and my Blackberry but will not send from Outlook. Receive is fine.

I have tried the smtp.mail.com with TLS and ports 587 and 25.

Each time I set it up, it will send a message, however when I try to send a second or subsequent message it get the 503 error message.

Can anyone help