1000s of emails per hour from WP – potential problem

I have what is essentially a website with jobs. I want to create a system whereby users can receive immediate notification when a job matching their criteria is posted.

Potentially this could mean that every job post made will send out several thousand emails! We post maybe 20 – 30 jobs a day but this could well increase.

I’m just starting to investigate this now, but how much impact is this going to have on the server? Am I likely to see a major degradation in the website speed and functionality with the server also sending out this many emails all day?

Just wondering what people’s thoughts on this are…

Thanks!