I too am having this problem, but fortunately I've found a workaround. According to the bug report, the issue has been fixed in a newer Modest build. Fortunately for us, Modest is open source, so I built a package of Modest 3.4.

I've only had it on my N900 for a few hours, but I've been able to do send and receive on my POP3 account without trouble, and I'm also able to get automatic notifications again.

To install my build, you'll have to install rootsh from extras, copy the attached package file to your MyDocs folder and then go into the terminal and enter these things:

1. Code:

   sudo gainroot

2. Code:

   cd MyDocs

3. Code:

   dpkg -i modest_3.4.1_armel.deb

The reason I'm going through all of this is because the package manager, for some reason, refused to install this package on its own, so it has to be done manually. I have no idea why.