Email relaying


I set up a web site for a friend on my server.  I also gave him an e-mail account using his new domain name.

When my friend tries to send e-mail through his dial-up "mom & pop" ISP's SMTP server using his new e-mail address, they reject it, saying they don't relay e-mail for the address he is trying to send to.  By contrast, my ISP gives me no problems when I do it.

Main question: Is there a way to safely let my server relay e-mail for him so he can send mail out using his new e-mail address?  I'm using postfix.

Curious question: It seems pretty restrictive to allow your users to send e-mail using only the e-mail address you give them as an ISP.  What's their problem?
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The question, as stated, isn't entirely clear as to what's happening. Is your friend using his dial up system and that ISP's mail server, but with a from address for his account on your system? Is he trying to send mail from your system via his ISP's mail server? Or is he trying to send mail from his dial system via your mail server?

In the first case above it may seem overly restrictive, but some ISP's do this a measure of spam control. A spammer isn't likely to reveal their true identify and by requiring the From to be an address valid on the mail server one can discourage this sort of activity. It will also block the majority of mail produced by viruses for the same reason.

If the problem is the first case the solution is to configure your mailer to allow your friend safe relay access via your server. The safest method is to configure the MTA for SMTP AUTH and have him use your MTA as the outgoing relay rather than his ISP's MTA.
nysus1Author Commented:
It's the first case.  I've given him a new e-mail address, with a domain on my server, called  He wants to send an e-mail to using his new e-mail address via his ISP's mail server but he can't do it.  His ISP's mail server says it won't relay mail for him.

I'm a little worried about the process of installing smtp auth, though.  I'm running postfix on a debian system and I'm pretty green.  I'd need a pro to do it right.  
It isn't erribly difficult. The procedure is covered in detail at Note that most modern distributions of Postfix are shipped with SASL enabled, but I can't say if that's true on Debian. You will need SASL installed and that may have happend by default when you installed the OS.

Try configuring SMTP AUTH in postfix.config and see if the SASL test shown in the docs works.
nysus1Author Commented:
Well, that's just it, Debian doesn't install it by default.  I don't even have all the required sasl packages.  And when I look around the web for advice for setting up postfix on debian I see conflicting instructions.  One says use cyrus-sasl packages and another says use libsasl.  So my head is pretty much spinning.  Plus, my knowledge of cryptography starts and stops with how public key encryption works.  So far, I have reilied on webmin to set up my e-mail accounts for me.  I have a long way to go before I get a clue.  If I'm going to do it myself, I'm going to be doing a lot of reading over the next week or two.

Thanks for your help.
Well, you could just follow the procedure from the Postfix site. That means building your own copies of Cyrus SASL & Postfix, but it should work as documented.

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