There is no reason why EE2.11.2 and Freeform 4.2.4 would work one day and not the next unless something has changed...
As it is (I am guessing) unlikely that you have changed anything in either the EE2.11.2 or Freeform 4.2.4 code, it sounds like something else has changed. It thus might be worth checking (for example) that nothing has changed on your server (e.g. php version?), or the configuration of your EE installation.
If that investigation doesn't flush any clues out, you could try double-checking your mail setup. You don't say how your EE installation connects to the mail service you use, but another thing worth trying is to change the mail service or mail server (or both).
Hope you find the problem. If nothing works, I would recommend considering another option - upgrading EE to the latest version - EE5 is so much better than EE2! The upgrade from EE2 to EE3 is a bit of a game, but much less so these days than it was when EE3 first came out - once you get to EE3 the upgrade to EE5 is usually pretty simple.