This is a feature and maintenance release.

• Multiple bug fixes for folding of long header lines, thanks to @caugner
• Add support for RFC2387 child element content-type hint in multipart/related structures.
• Support for Ical event methods other than REQUEST, thanks to @puhr-mde
• Change header folding and param separation to use spaces instead of tabs
• Use ; to separate multiple MIME header params
• Add support for RFC3461 DSN messages
• IMAP example code fixed
• Use PHP temp streams instead of temp files
• Allow for longer SMTP error codes
• Updated Brazilian Portuguese translation
• Throw exceptions on invalid encoding values
• Add Afrikaans translation, thanks to @Donno191
• Updated Farsi/Persian translation
• Add PHP 7.4 to test config
• Remove some ambiguity about setting XMailer property
• Improve error checking in mailing list example
• Drop PHP 5.5 from CI config as it's no longer supported by Travis-CI
• Fix S/MIME signing
• Add constants for encryption type
• More consistent use of constants for encryption, charset, encoding
• Add PHPMailer logo images