I recently set up a Citadel installation on my Linode, and while I am not having any trouble send emails outbound I am having a lot of trouble receiving emails. I am fairly certain the issue is DNS or Citadel configuration related but nothing I have tried has had an effect on the results.

I am able to email my users at:

user@mail.domain.com

but if I try to use

user@domain.com

I receive the following notification: (being sent from Gmail)

Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 550 550 Invalid recipient: user@ (state 14).

All outbound emails are @domain.com, not @mail.domain.com and they have no problems.

My DNS records with Linode are all default except for an added MX Record, making my MX records as follows:

@ MX 10 mail.domain.com.
@ MX 10 domain.com.

Within my Citadel configuration I altered the fully qualified domain name from host.domain.com to domain.com. This allowed me to successfully create users with email addresses @domain.com by default.

Under Local Host Aliases I have both:
mail.domain.com
domain.com

Could anyone advise me as to what I could be missing in my setup? Any help would be greatly appreciated.

Managed to resolve the issue.

Apparently when I created the test user the domain name for the system was still set to host.domain.com. By deleting and recreating the user with the domain name set to domain.com, or by adding an alias, the problem was solved.

Nice catch. I've found that when editing a user, Citadel likes to change the user's "Primary Internet e-mail address" to what it thinks is correct. It might not be.

If editing a user make sure to use "Edit address book entry" and validate "Primary Internet e-mail address" is right.

That and the "rooms" concept are odd but in general I like Citadel, easy to set up and administer.

Here's the real crazy trick: The primary internet email address WAS correct. I had changed it to domain.com from host.domain.com.

I added an alias that matched the primary address of domain.com, and only then did it start to work.

I believe there was some disconnect between what I was seeing and what it actually had stored as the user's primary address.