[Dovecot] version question

[voytek at sbt.net.au]

I have Dovecot server from a iRedMail install, version 2.0.21

dovecot --version
2.0.21

yum update wants to update as so from iRedMail repo:

--> Running transaction check
---> Package dovecot.x86_64 1:2.0.21-0_136.el6 will be updated
---> Package dovecot.x86_64 1:2.1.17-0_136.el6 will be an update
---> Package dovecot-managesieve.x86_64 2:0.2.6-22.el6 will be updated
---> Package dovecot-managesieve.x86_64 2:0.3.6-26.el6 will be an update
---> Package dovecot-pigeonhole.x86_64 2:0.2.6-22.el6 will be updated
---> Package dovecot-pigeonhole.x86_64 2:0.3.6-26.el6 will be an update
--> Finished Dependency Resolution

 Package                       Arch             Version                   
     Repository          Size
=========================================================================================================
Updating:

 dovecot x86_64 1:2.1.17-0_136.el6              iRedMail           2.4 M
 dovecot-managesieve x86_64 2:0.3.6-26.el6      iRedMail            45 k
 dovecot-pigeonhole x86_64 2:0.3.6-26.el6       iRedMail           348 k


so, if I run this update, I'll update to '2.1.17-0', yes ?

ahem, dumb question ahead: what's the '1' in front ? 1:2.1.17-0_136

(dumb user worrying that I don't attempt to install ver 1...)

apart from /etc/dovecot/*, should I backup anything else ?

sorry for dumb q...

thanks