I am having an odd problem when sending mail with an external mail client (thunderbird) through my server (CentOS 4.4) running exim 4.63. When sending mail to external domains NOT hosted on my server, such as to hotmail email's, the email is accepted and sent through immediately. However when sending mail to domains that ARE hosted on my server, such as my own domain, it takes upward of 30 seconds for the email to finally be accepted and delivered. Thunderbird will just sit there at "connected to mail.eggycrew.com" until it is finally sent.
I've done a bit of research and haven't found anybody having this issue before. Any ideas?