Maybe a poor soul with the same problem will Google for the error message and find this entry.

Been trying to find a web based email client that uses IMAP written in PHP. I'd use Squirrelmail, but apparently it does some stuff that PHP5 doesn't like. At all. If I can't find one, I'll write my own. But I found a few half-baked clients that use the imap_*() functions in PHP.

However, when I enable extension=imap.so, I always get /usr/sbin/apache: relocation error: /usr/local/lib/php/20040718/imap.so: undefined symbol: ssl_onceonlyinit.

I googled for it, and found this article. It's in German, but essentially it says to try installed libc-client-ssl2001. So I went ahead and did apt-get install libc-client-ssl2001-dev anticipating that I'd have to recompile PHP. But I didn't. It installed the two packages, I restarted Apache and that was that. Cool deal.