I have mail server on slackware 12.2 sendmail and imapd. This is a home server so I used only 512MB memory.

Several days ago I started have troubles with downloading of zip compressed attachments (thunderbird configured for IMAP account).
I didn't find anything strange in logs.
The mailserver works. The problem is when I start downloading of attachment in zip it downloads several Kbytes and it stucks.
And on the local network it works fine.

The only strange thing I find is that when the server is after restart the used Memory is 186000k. When I start some mail client (thunderbird) and open the inbox the used memory jumps to 440000k. I didn't compare these values before this. Is this normal?

What can be the problem with the zip attachments?

Added: 7.aug. 9:55

I cached the communication by wireshark when thunderbird starts and there are lots of malformed packets sent from server side.
In the packet details I can see:
When I turn off SSL on thunderbird there are no malformed packets.

You haven't mentioned if after switching off SSL, whether the problem with downloading zip attachments still happens. Have you checked your total system memory usage with:

free

Is swap starting to be used? How much memory is the imapd server using? Are you running it out of inetd or as a standalone server?

Do you only have problems with zip files? Or other attachments?

If the attachments work fine inside your network but not from external, then perhaps you have a firewall issue. You could also have a faulty network adapter or problematic hardware somewhere. Check also whether your negotiation settings on your network adapter are ok for your network ie. speed, duplex, etc

Check all system logs ( debug, syslog, messages, maillog for errors ) as well as dmesg.

Robby

Yes after I turn off SSL the problem is still present. I think that with memory it will be OK. The Swap is used.

I run imapd by inetd: it uses 0.6 % of memory
It happens only with zip attachmets others pdf, exe ... everything works.
It really looks like that it will be some kind of network problem (BUT). I tried download the attachment on my home slackware desktop and it worked without malformed packets, BUT it tells me something like this:
invalid filename
Invalid byte sequence in conversation input

The attachment was named - Nový Priečinok.zip - what means New Folder.zip in Slovak. After I saved it under different name (data.zip) it woked.
It seems to me that the same happend on my work windows PC but it didn't show the error message what slackware did.

Next- the problems started after a stormy night when my PC's was shutting down every 5 mins (thunder-bolts). My server is protected by surge diverter protection (?? I don't know if I named it correctly) but the router is not.
I am going to examine my router.

few hours later:
So it really seems to be the ADSL modem problem. I have logs from the router about ADSL status before (and after) the storm:
My ISP increased both the download and the upload speeds. I experienced several times with our internet provider (Slovak Telecom) that they had to reconfigure the speeds when there was a problem with the connection. Usually they decrease the speeds.
I will call them up and ask them to check it.
Maybe when the attachment starts to be downloaded it overloads the upload speed and the connection freezes.(??)

Thanks Robby

Zoltan