Few comments:

- SASL support is in experimental stage. Use it with caution. It's rather
  hard to use it in production.

- You should upgrade your Cyrus SASL library to at least 1.5.24 version.
  Earlier versions (1.5.21 for sure) have nasty security bug. There is
  workaround available in Solid POP3, but it's disabled by default.
  You can enable this workaround by changing "0" to "1" in line 333
  in src/spsasl.c file, but upgrading Cyrus SASL is a better idea.

- SASL database should be readable for "spop3d" user.

- You can't use user mapping with SASL.

- You can't use domain-per-uid mechanism with SASL
