Postfix Down for Lengthy Periods

[Casket88]

Three to four times a day i will get calls from multiple users stating they can no longer access their emails, when this happens every single user accross the country (including those on the same network as the Postfix server) endure the same problem.

Using Thunderbird as a client, when you click on "Get Mail" it will say in the bottom left hand corner:

Connect to x.x.x.x....
Connect: Host contacted, sending login information...

It will sit like this until it times out. Running wireshark and getting a cap of this stream shows the following packets:

Client: SYN
Server: SYN/ACK
Client: ACK
Server: Response: +OK Cyrus POP3 v2.2.12-OS X 10.4.8 'mailserver' Server Ready
Client: Request CAPA
Server: ACK
Server: Response: +OK list of capabilities follow
Client: Request: User 'username'
Server: ACK
Client: FIN/ACK
Server: ACK

This shows there is connectivity with the mail server. The delay before the servers ACK to the username and the clients FIN is roughly 2 whole seconds. The server simply will not return the clients mailbox.

This has been going on for months. The problem usually goes away after a while but we have reached a point where something needs to be done about it.

If anyone has any suggestions about the best path to take to recify this problem please let me know.