Change url's to links on out going emails

Hi I’m building a site that I want to offline on localhost urls. Now thats fine. But when the user gets and emails it has the localhost link. I need to change it to the live website link or obviously they won’t get to where i want them to go.
Is way to do this?
I’m also reading into mysql replication to keep my two databases in sync and feedback on that would be appreciated also.

Doing it this way as I am a contractor and I am using sprout invoicing plugin so i basically will be using a tablet to do my invoicing on the job site and I don’t want weak web connection to affect the operation of the site. I understand php / javascript / I’m new to wordpress but its starting to make sense.

Thank you!