No emails being sent

I recently discovered that my self-hosted site is not sending out confirmation emails to new users and that the Contact Form 7 plugin is inoperative. Not sure if this is a wordpress or an apache issue.

I came across this post: https://www.ads-software.com/support/topic/268487?replies=2 which may e the same problem I’m having but I’m not sure how to go about resolving it.

Any advice?