[Dovecot] Dovecot performance under high load (vs. Courier)

[Wojciech Puchar]

>
> We are building a new system that will support a large number of users (high volume, high concurrent usage, etc).
what is large?

>  We have played with Dovecot, but in most serious applications we have traditionally used Courier IMAP.
>  It's my (lay) understanding that with indexing and perhaps other things 
>in Dovecot, it might perform better than Courier in larger environments 
>like this.  Am I correct or is it less clear-cut?

No idea how well courier IMAP performs. But have idea how well dovecot 
performs. I don't have large configs like thousands of users as i don't 
handle "herd of random users" style cases, but in every place i have 
dovecot IMAP takes unnoticable amount of server load.

Just make a test.

Definitely use maildir format, not mbox.

dovecot heavily accesses it's index files. they are not large relative to 
e-mail sizes. With really large case if I/O will limit you i would 
recommend using SSD storage to keep just indexes.