The Register posted an article about a follow-up on the Mail.app issue with the Mac 10.5.6 update.

The bugs that users experienced when they upgraded to the operating system version is due to “outdated third-party Mail plugins” according to Apple’s security bulletin.

The Register includes includes an instruction on how users could fix their problems with their email software. The instruction include checking whether Mail is up to date and whether its plug-ins are fresh and healthy.

The article includes another solution which is an Archive and Install reinstallation of Mac OS X 10.5(preserving settings) after users backed up their files.

Source: The Register