Simple Email System (SES) Provider

Hi all, I built a system in PHP/mySQL where a group of users post events, sign-up for events, change their arrival times, remove thier names from events, and post related notes on the events. Each time an action is done, an email is generated to the entire group that their has been a change. Pretty standard stuff... Today I just got an Mail Delivery System email with this error: Domain dwdcweb.info has exceeded the max emails per hour (350/350 (100%)) allowed. Message will be reattempted later I contacted my VPS provider and they just alerted me that there is a limit on how many emails my server can send per hour. They recommended I find a 3rd party service provider with support PHP API connections. My budget is limited. Does anyone have any suggestions of companies that might work for my scenario? Any feedback is appreciated ;-) Don