[MlMt] Updating account information made MailMate (re)download *all* email

[Sherif Soliman]

This happened on the MailMate BETA, but I don't know if it's limited to 
it or can happen in the stable version.

I use FastMail and they recently made some security upgrades[1], which 
include two factor authentication (2FA), app-specific passwords, and new 
imap and smtp server names.

[1]: 
https://blog.fastmail.com/2016/07/25/two-step-verification-and-other-new-security-features/

Once you enable 2FA on FastMail, you *have* to generate app-specific 
passwords. I generated a new password for MailMate to use, and went to 
update the account information by right clicking on it in the list of 
sources.

I put in the new password and changed the server names from the old 
`mail.messagingengine.com` to `<protocol>.fastmail.com`.

What happened afterwards is that MailMate re-downloaded my entire email 
content from FastMail. I know because I use Little Snitch and I could 
see that MailMate used the same amount of bandwidth down as my used 
space on FastMail.

It also reset some of the mailboxes that have "types". For example, I 
had to re-tell MailMate which folder to use for Sent Messages, and which 
one to use for Junk, and Trash.

I don't know if that's expected behaviour or not. It could be a really 
expensive download for some people (I have the speed and bandwidth to 
spare, so I'm good).

If it is unexpected but intended, is there a way to make it not happen?

If it is unavoidable for whatever reason, then this is a PSA to people 
that this could happen, so if you plan on making changes to server names 
and can wait for a time when you don't need your network or have free 
bandwidth, you should do that.

Sherif