Last days we can see a lot of SMTP_DELIV_FAILED in our logfiles
Looks like there are out many mailservers using a spamfilter solution that blocks all incoming smtp traffic if the sender domain cannot be resolved.
They shouldn't -- it's a very, very bad thing to do. But there are so many anti-spam companies popping up, many don't know good from bad. :(
But there is also another problem: We set up all our virtual mail hosts in the form mail.clientdomain.com and the alias clientdomain.com So all webmail users have a default sender address of [EMAIL PROTECTED]
That should be fine. It's unfortunate that Ipswitch doesn't have two settings (one for web messaging that should be "mail.example.com" and one for E-mail that should be "example.com"), but that will work fine of mail.clientdomain.com has an MX or A record pointing back to the IMail server (otherwise, replies won't come back).
Now all messages send from webmail with the default sender address are blocked from this receiving mailservers.
Not because of the return address.
Solution: A.) Manualy remove the "mail." for every mailbox user
That won't help. "[EMAIL PROTECTED]" is perfectly valid. If someone blocks that, they will almost certainly also block "[EMAIL PROTECTED]" (thinking the address should be "[EMAIL PROTECTED]").
B.) Add an A- or CNAM-Record "mail" to any DNS-zone of all clientdomains
That's not necessary either. If you already have an MX or A record for mail.example.com, then your mail should be accepted. If not, there's a problem on the other end.
So it's now legit to block any mail having an invalid sender domain or is this the "idiots way to filter spam" ?
Most people consider it legitimate to block mail having an invalid sender domain -- but, the reason for that it that replies will not go anywhere (why read an E-mail if it is impossible to reply to it?). In your case, I'm assuming replies will go back to your server, in which case the mail should not be blocked.
-Scott
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