Maildir filename parsing questions

[mcSmartyPants]

Hi, I haven't found any references to this, so I'll ask:

I'm using RC + dovecot + postfix. Mail messages get created/stored in the user's Maildir "new"/"cur" folders. I'm wondering how much info I can glean from the filenames, to do some statistics without invading privacy.

So, for example, I'm pretty sure that ",S" gets appended when a message is marked as Read... What other predictable characters are there?

Example:

• 1543626953.M281022P21036.mx1.musicplace.com,S=188628,W=191393:2,FS

I'm pretty sure that:

• 1543626953: unix epoch timestamp
• M281022P21036
• mx1.musicplace.com: hostname of the mailserver
• S=188628: filesize in bytes
• W= maybe bytes on disk???
• ":"  a delimiter
• 2,FS

But the bit I"m really interested in is after the ":", which is often "2," with additional letters. Anybody know what they mean?

TIA,

[alec]

https://en.wikipedia.org/wiki/Maildir

[mcSmartyPants]

Thank you so much alec - that's really helpful!