Once your email outcoming protection is enabled, all your mails are relayed trough Perimeter. So to avoid delivery problems you need define properly your SFP record on yours DNS to include perimeter servers as allowed to relay mails from your domain name.

You need add: include:spf.perimeter.email and change your restricton tag from -all to: ~all

Tipical "v=spf1 +a +mx -all" record should be changed to:

"v=spf1 +a +mx include:spf.perimeter.email ~all"