You're going to want to describe how you have your mail client configured in (far!) more detail, imap or pop, whether you're using authenticated (you should be), what your network connection looks like, whether this is on-LAN or remote, etc., and you'll also be checking your server logs in parallel.
That "(null)" as the name of the server is particularly interesting. Odd. In addition to the topology, what does your local DNS look like here?
OK, was hoping to spare you the gory details and hope it was an obvious problem...alas...Here ya go:
Authentication is handled at login (single sign-on) by Kerberos Version 5 (GSSAPI)
Very simple network. Clients connected to server through hub via Ethernet (LAN)
Router also connected to same hub (and DSL modem is connected to router)
Forward (& Reverse) DNS resolves for both Client & Server w/in the LAN.
Client is using the Leopard Server for all its DNS (was necessary to get Kerberos working ages ago).
Everything works fine except sometimes Mail.app throws this alert.
BTW - At least 8 different mail accounts handled in this Mail.app (3 POP, 5 IMAP (incl 1 MobileMe), but only this Leopard Server account throws the alert. (Well, there's a Tiger Server out there on the Interweb that throws an alert much less often but that's when that office has a power failure or something).
Message was edited by: Demetrios
Most likely this is a limit on the maximum number of concurrent connections allowed to your mailserver.
Mail.app makes a lot of simultaneous connections (open the activity window and see). So you will need to set up your mailserver to accommodate this.
Also, when collecting mail on its regular schedule, mail.app attempts to access all your email accounts simultaneously. So every email address generates multiple connections to the server. So the problem multiplies.
If you are able to set the maximum number of connections (total) and the maximum number of connections per ip address to larger numbers, then the problem should disappear. The numbers will depend upon the the number of people who are accessing those email address, the number of email addresses and the number of unique IP addresses in use.
I needed 200 (max) and 50 (max per ip).
Hope this helps.
Expr3ss! how many mail accounts do you have? I've tried bumping my my connections up to seemingly insane numbers (600 daemons, 300 maxperip). I only have 9 mail accounts.
This hasn't made any difference. If I hit "get mail" quickly I'm able to get all the mail eventually, but I can't be needing to click get mail 20 times each time I want to check all.
These problems all surfaced when upgrading to snow leopard and ilife 11.
MY SOLUTION REPOSTED FROM ANOTHER THREAD:
I've just solved a similar issue.
I have a dedicated server running Plesk 9.5 and when I upgraded to iLife 11 and Snow Leopard this error appeared. I could quickly click "get mail" and I'd get all my mail, but only 3-4 of my 9 mail accounts would connect. Theo others would have the error:
"The server error encountered was: The attempt to read data from the server..."
I found solutions for those using IMAP mail:
modify the /etc/courier-imap/imapd configuration file and change MAXDAEMONS from 40 to 80 and MAXPERIP from 4 to 40. This allows all the machines behind my home firewall to connect to multiple accounts on the e-mail server with mailbox caching enabled.
I'd made this change on my server but it didn't seem to have any effect. It dawned on me that I'm using POP, not IMAP. So I found in /etc/courier-imap/pop3d the same settings. I changed the MAXDAEMONS from 40 to 80 and MAXPERIP from 4 to 40 and voila, all my connections concurrently worked.
This has taken me more than two days to fix and I hope posting this helps someone else with the same issue.
Thank you, thank you, thank you.
This solution to IMAP issues has saved my sanity. I've been battling with irritating alert symbols in Mail and spotty connections for a year now and by chance I found this post of yours. I've logged into my server, changed the values, and all seems good so far.
All the best,
modify the /etc/courier-imap/imapd configuration file and change MAXDAEMONS from 40 to 80 and MAXPERIP from 4 to 40...
Can you please be more specific - modify using which tool?
The server I am trying to connect to always gives me this error message: