Scott Morrison has released a new public beta of his IMAP-savvy MailTags 2.0 plugin.
Public Beta 10 introduces the ability to turn off the automatic saving of tags to IMAP servers and to manage it manually. It also fixes numerous bugs, especially issues related to smart mailboxes and “to do”-related criteria.
Since tagging IMAP messages can create extra bandwidth usage, there is now an option in MailTags’ Preferences to switch off the autmoatic saving of tags to the IMAP server. This preference is on by default. Turning it off means that tags are only saved to the local cache files. You save bandwidth, but the tags are naturally not available to other computers.
For added fine-tuning, you can choose not to save tags on messages over a certain size:
When a message has tags that are only saved to the local cache, an extra button “Save To IMAP” appears at the bottom of the tags panel.
Clicking this button will immediately save the locally cached data to the IMAP server. A similar option appears in the MailTags menu and in Mail’s Contextual menu. Or you can just highlight the message and press ⌃⌘S.
Given Scott’s trademark attention to detail and completeness, a new criterion has been added for smart mailbox configuration: “IMAP Tags are/are not saved to server”.

A new icon in the MailTags column quickly indicates which messages have tags saved to the IMAP server or not. The messages with the orange tag icon have tags saved locally only:
Lastly, as extra insurance, tags not saved to the IMAP server are retained during mailbox rebuilds.
The latest public beta also contains a bucketful of bugfixes. The interface has been firmed up, HUD windows are better positioned, and customised MailTags columns behave better in the Mail Viewer.
Smart Mailboxes based on To Do items, especially on completed items, are smarter and will now work as expected, although you may need to reindex your tags using the new “Reindex Tags” option in the Preferences).
To dos now display using the user’s internationalization (or internationalisation) settings. Huzzah!
MailTags and iCal now mutually update deleted to dos and events more consistently.
Rules management has also been further improved. Two potential crashes when applying or editing rules have bene corrected, and rules are more efficiently applied.
Users with Dovecot IMAP servers will be glad to hear that MailTags no longer overwrites its X-Keywords headers when rebuilding mailboxes.
MailTags’ SpotLight importer has been updated to take account of new to do counts, completion status and IMAP save status.
This long list only picks the best bits out of a much longer changelog 
on the MailTags web site.
You can read more about MailTags 2.0 and download the new public beta from Scott’s web site , where you will also find a forum for any questions.
I’ve installed MailTags twice now (once a couple days ago and once about a year ago) and both times after installing I immediately noticed that messages on my IMAP server didn’t stay marked as read consistantly.
Has anyone else noticed this or is it something particular about my setup?
I have not noticed with MailTags but did experience, and still do, this problem whenever I install the GPGMail bundle plugin.
Hrm … I use GPGMail as well, in this case I removed both GPGMaIl and MailTags at the same time so I could have confused the symptoms.
However I wasn’t having problems with GPGMail installed before I installed MailTags. I shall investigate more throughly, thanks for the sanity check.
Adam.
I’m sure this is covered somewhere… does MailTags actually use IMAP keywords? That is, does it use the IMAP protocol to store those keywords? Or does it dump the keywords into a message stored in a hidden folder on the IMAP server? Or does it just modify message headers? (remember that IMAP servers like Courier do not store keywords in the message; they’re stored in separate index files in each folder)
From page 21 of the User Manual …
How do MailTags 2.0 differ from IMAP permanent flags?
Many IMAP servers have the ability to apply keywords (or flags) to messages. These flags work differently than MailTags in several ways. First and foremost, MailTags will write its data to the headers of the message. While this involves more interaction with the server, indev believes that most messages are small enough and most connections with IMAP servers are fast enough to minimize performance issues. By having data in the headers, MailTags can store and organize data much better, separating keywords from projects, allowing for
dates, notes and keywords that include Unicode text.