Email ports

Email setup and troubleshooting
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Email ports

Post by Mortq » Thu Feb 04, 2010 10:50 pm

I have a work email account, which I use from home using Thunderbird. The official advice from work is to use smtp settings that include using Port 587 and a name and password with connection security set to SSL/TLS. They advise that using port 25 (which is what we use at work from the LAN there) won't work from home as many ISP's block it.
My experience is that port 25 works with my exetel connection, but port 587 results in an error message:
"An error occurred while sending mail. The mail server responded: 5.7.0 No AUTH command has been given.. Please verify that your email address is correct in your Mail preferences and try again."

Does exetel allow mail to an smtp server via port 25, but not other ports, or is something else going on? (This isn't a big problem, as my email is working, I am just wondering why the difference from what works for others with different ISPs, and I don't know enough about email and its protocols to understand what is happening myself.)

Thanks, Mort

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Re: Email ports

Post by Dazzled » Thu Feb 04, 2010 11:01 pm

Exetel doesn't block ports. Your TB config probably has the wrong secure connection authorisation for the mail server.. Just stay with what works.

PS Do you use Windows? If so, check your firewall/malware suite.

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Re: Email ports

Post by CoreyPlover » Fri Feb 12, 2010 2:20 pm

Port 587 for email is a relatively recent thing that is an attempt to cut down on spam. Here is a primer:

Most ISPs have configured their web server to listen for email messages and requests on port 25 (as Exetel do). Exetel also have a security setting that dictates a few things to reduce spam:
  • You need to be using an Exetel connection to access SMTP
  • You need to authenticate using your credentials
  • If Exetel detect spam coming from your system, they blocks your internet access automatically
Most other ISPs don't have all or any or the above. What this means is that if a virus gets into your computer, it can start sending out spam emails. So one recommendation that security experts are starting to call for is for ISPs to block port 25 and to instead configure their email servers to use port 587. The difference: Port 587 requires a secure authorisation and encryption. This makes it harder for spam be sent out.

So: Most ISPs use port 25 and don't prevent outgoing spam at all (shame on them). Some ISPs (as your work knows) block port 25 and use 587 instead. But Exetel use port 25 and block / detect spam in a different manner.
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