Mail stuck in mail queue

[flyingstar16]

I'm running ZCS

Release 5.0.10_GA_2638.DEBIAN4.0 DEBIAN4.0 FOSS edition

associated with a subdomain of my company and, until a couple of days ago, e-mails were correctly delivered.
Now, I can see 13 mails stuck in the mail queue (deferred), which means that mails arrive on my machine but Zimbra cannot deliver them into the right mailbox
From Zimbra, I can send e-mails, but nobody can receive.
Can you help me?
Claudio

[flyingstar16]

Update:
problems started when I changed my servername via zmsetservername, in order to reflect the dns name (e.g. I changed Zimbra's machine name from debsrv2.dev-mydomain.com to dev.mydomain.com).
I did not regenerate certs, but I could access zimbra from everywhere, allowing connection when my browser noticed that there was a problem.
My question is: what do I have to do in order to make Zimbra work when I change my servername? (yes, I want to change it: otherwise, everytime I want to check e-mail folders from zimbraAdmin I have to manually change the URL in my address bar; stupid thing, but it annoyes me)
Thanks!

[irfan]

Have you modified your MX record to point to new name of the server?
Have you put an correct entry for servername and its correct ip address in /etc/hosts file?

[flyingstar16]

My MX record points is not a problem, because nameservers are external (i.e. my MX record points to an A record that's bind to a static IP address, that is not changed).
Neither the LAN address of the machine is changed (it's 10.0.0.11) and my /etc/hosts looks like this (assumed that "machinename" is the name of the machine zimbra is running and "my.new.address" is the A name of the DNS and my server name (set via zmsetservername))

127.0.0.1 localhost.localdomain localhost
10.0.0.11 my.old.machinename machinename my.new.address

I have tried putting "my.new.address" near to localhost (bind to 127.0.0.1), but no way

[irfan]

Modifing hosts file like this might help:

127.0.0.1 localhost.localdomain localhost
10.0.0.11 my.new.address mynewhostname
10.0.0.11 my.old.machinename machinename

[flyingstar16]

I had tried, but /var/log/zimbra.log continuously said "Timeout while connecting to my.new.address" (even after restarting Zimbra).
(I don't remember what was the exact error message, but I do not have all-week access to Zimbra's machine, sorry)
BTW, thanks for helping me - I know it's a not-so-important problem

[uxbod]

if you could post the following it would *really* help us

cat /etc/hosts
cat /etc/resolv.conf
dig yourdomainname mx
dig yourfqdnservername
host `hostname` <- note backticks and not double quotes

it is okay to obscure your domain name if you wish but please leave everything else intact.