A few things to check:
-- check and see if any emails at all are getting out; try sending one to yourself through the system by looking yourself up in the Journal Management -> Roles pages (you'll find an email icon next to your name).
-- check with the email service provider, in this case Google Apps, to see if anything has changed configuration-wise, or to see if they are experiencing problems on their end.
-- double-check the email logs on the system, especially the submission history email logs, to see if there is a record of these emails going out. If not, please let us know exactly which email this is.
-- Let us know which version of OJS you are using, whether you have recently upgraded and/or whether the server software (eg. Apache; PHP) was recently upgraded.
If both of you are only recently having problems, and are both using Google Apps as the mail server, I suspect that the problem is with Google Apps -- you should be able to follow up with them to see if anything has changed wrt their software offerings.