Sendmail /Perl - Is there a dns check when sending ?

Greets,

I need help on this one, am not familiar with sendmail per se. We're using a perl-cgi to send mails (in BCC) to a list of users (It's on an old reworked Serverside javascript site...had to resort to sending mails with a perl cgi because the SSJS sendmail() would fail sometimes. The box is running on Solaris)

The script was working fine through the testing phase, but has been locking up today (harrrr!). We haven't changed the script, and found no SSJS errors in the logs, so I'm thinking about sendmail being the issue right now. I've noticed we've had trouble sending/receiving external mails for the last couple days(not only using this box, but multiple ones, including the big commercial ones like hotmail, Imail etc). So, here's my question:

When sending mail with a list in BCC, does sendmail do a check for each domain before passing to the next one? I'm sorry if it's a silly question, but am pretty much a noob in sys matters....

Help greatly appreciated