I use my Linode as a web host only, and use Tuffmail for my email needs. Accordingly, I have my MX records pointing to Tuffmail. Anyway, it appears that when I send an email via sendmail or php's mail function, I can send to any domain EXCEPT for my domain. I am sure it's some simple config issue, but I am stumped. Any ideas?

A little more information would be helpful, what mail server are you using? Are there any errors in /var/log/mail.log

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odd, it works for me

Your mail system (postfix maybe?) may think it is authoritative for your domain, so it isn't bothering to do MX record lookups to deliver mail.

Mar  9 04:33:36 localhost sendmail[3644]: p29AXaTm003644: to=user@domain.com, ctladdr=user@domain.com (33/33), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30532, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (p29AXaab003645 Message accepted for delivery)

Mar  9 04:33:36 localhost sm-mta[3646]: p29AXaab003645: to=<user@domain.com>, ctladdr=<user@domain.com> (1000/33), delay=00:00:00, xdelay=00:00:00, mailer=local, pri=31003, dsn=2.0.0, stat=Sent

I actually do not have a mail server set up on this installation. (Though I do use sendmail and php mail for outgoing mail only).

You should probably follow one of these guides then

http://library.linode.com/email/exim/se ... 0.04-lucid
http://library.linode.com/email/postfix ... 0.04-lucid
(assuming you're using ubuntu lucid if not pick the relevant guide from the library)

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Thanks for the links! I followed the first guide, and unfortunately I am still having the same issue. My username is the same as my email address, so email is being delivered to my user instead of being relayed externally. Any other ideas?

Edit

/etc/exim4/update-exim4.conf.conf

and set

dc_other_hostnames=''

then run

update-exim4.conf

and then

 /etc/init.d/exim4 restart

_________________
Paid support
How to ask for help
1. Give details of your problem
2. Post any errors
3. Post relevant logs.
4. Don't hide details i.e. your domain, it just makes things harder
5. Be polite or you'll be eaten by a grue