sendmail.cf

we have two mail servers and want to setup failover for DR.

we have a line in sendmail.cf like this

DS smtp.domain.com  

and this works fine......

we changed it to

DS smtp1.domain.com smtp2.domain.com

this is bad, we get errors of savemail panic and many bounce messages and such. the errors say cont find server smtp1.domain.com.smtp2.domain.com

our two solutions to the problem are

version 1

DS [smtp1.domain.com] [smtp2.domain.com]

version 2

DS smtp1.domain.com:smtp2.domain.com

both seem to work but I assume that one is more correct than the other.
looking for some education as to what the diffcence is.

I don't know if " : " would work, but putting "DS[smtp1.domain.com]" will disable MX record lookup, so this should be valid.