[GTALUG] war story: Thunderbird needs to be told to compress its folders

[D. Hugh Redelmeier]

TL;DR:
	If you use Thunderbird, once in a while, do this:
		File: Compact Folders

	This may be the only way to get space back
	for deleted messages (I'm not sure).

Now for the war story.

One of us uses Thunderbird to read mail.
It stopped working yesterday, with no useful diagnostic.
In particular, it would no longer pick up mail from our POP3 server.
There was no signal to the user.

I looked in the Error Console (meant for developers, not users) and
saw two messages, the first being:
  tb.account.size_on_disk - Truncating float/double number.

What does this mean?

First guess: Javascript stores numbers in 64-bit IEEE 754 floating
point representation.  A large integer may not be precisely
represented.  But there are 52 bits for the fraction AKA mantissa and
2^52 is very very large.  My mail files were at most a small number of
gigabytes - perhaps 2^32.  So this cannot be the explanation.

Googling didn't help: the message showed up in posted logs but wasn't 
relevant to failure to fetch mail.  Still, some did suggest that a
Compact Folders command was in order.

About three gigabytes of space freed and the first message
disappeared.

<https://support.mozilla.org/en-US/questions/1391958>

We still could not pick up mail.