[exim] Queue ID format

Hello,

I'm parsing Exim log files, specifically the mainlog. Man, that's a
complex structure and it's hard to find all necessary details from the
documentation and by reading my actual log files. I'm using several
regular expressions for different kinds of lines. But a stateful parser
(the ones used to understand programming languages) would probably have
been the better choice here. Apache access logs just require a single
regex, for Exim I already have 8, one of which just covers most
meaningless messages I don't care about, and lots of detailed
post-processing.

What assumptions can I make about the format of a queue message ID? For
now, I use this regex:

[^ ]+

Though it seems they always match this regex:

[0-9A-Za-z]{6}-[0-9A-Za-z]{6}-[0-9A-Za-z]{2}

Is this correct? Google couldn't tell me.

-Yves