As per our earlier blog post about Magnet’s Simply Broadband – we forgot to mention that Magnet blocks TCP Port 25 outbound on it’s residential accounts.
Their solution is to change the SMTP server to theirs: smtp.magnet.ie
In some cases, this is not suitable. You can try changing the outgoing port to 26 – some hosting companies, such as Spiralhosting, offer this facility.
The other solution is to use SSL SMTP – port 465.