Simple Mail Service mail quota per second query.

My question is what will happen if two or more our customers will press "recover email password" at the same time.

**We have sending mail quota 1 per 1 second. **

Only one of two customers will get email, or others will get it seconds later? Is there a sending queue in Amazon Simple Mail System, or emails exceeding quota are just not sent?

Sorry for probably simple question but can't find answer for it easy.