You really should consider taking a look at the detailed release notes for version 1.6 of MailMate since a lot has happened since version 1.5.4. Just in case you are in a hurry then here are the condensed highlights:

  • “Send Later” feature added, for example, write “2 hours” to delay a message or “friday at 12.00” to send at a specific time. Read more here.
  • New mailbox editor with multiple panes including “Submailboxes” for configuring automatically created submailboxes. Read more here.
  • New view showing tips about some of the less obvious features of MailMate.
  • Live preview in the Composer window (no longer just updated on Save).
  • Improved the (extended) mailto: scheme.
  • Built-in support for decoding TNEF files (winmail.dat).
  • Support for decoding the x-uuencode transfer encoding. Important for attachments in messages generated by certain older email clients.
  • Now showing the URL target of a tooltip when hovering over a link.
  • Added a “Reply All” toggle to the composer toolbar. It works as both a toolbar button and as a shortcut (both ⌘R and ⇧⌘R works).
  • De-obfuscation of email addresses when pasting text in a recipient header, for example, user at example dot com becomes user@example.com.
  • Markdown support includes footnotes.
  • Much faster at displaying long text messages.
  • Various IMAP fixes including a workaround for a problem with Gmail causing sent messages to have duplicates in the drafts folder.
  • Numerous other fixes making MailMate even more robust than it already was.