This is a maintenance release. The changes introduced in 6.3.0 for setting an envelope sender automatically when using mail() caused problems, especially in WordPress, so this change has been reverted. It gets a minor version bump as it's a change in behaviour, but only back to what 6.2.0 did. See #2298 for more info.

Other changes:

• Check for the mbstring extension before decoding addresss in parseAddress, so it won't fail if you don't have it installed
• Add Serbian Latin translation (sr_latn)
• Enrol PHPMailer in Tidelift, because supporting open-source is important!