Catalina has more restrictions on system folders which we can apply an exception:
Open System Preferences -> Security and Privacy -> Privacy tab -> Full Disk Access -> Press 'Unlock to make changes' padlock
Open Finder Window -> "Go" menu -> "Go to folder" -> type "/usr/sbin/"
Drag the file "httpd" to the list inside the Full Disk Access settings.
Also had Apache not starting after upgrade to Catalina. I had my websites originally located in subfolders of the /Users/***/Sites/ folder, and according to this thread, made a new folder /Users/***/Repos and moved all websites there and updated MAMP Pro doc roots for all hosts. That didn't allow Apache to start.
After that, I found this info:
Check your ...
I have the same issues. Updated MAMP to the latest build (5.5). Also switched the ports back to MAMP default ports (8888). That worked for me. Also checked if some diffrent server was running on port 80 lsof -nP -i4TCP:80 | grep LISTEN but nothing seem to be using port 80. Could it be Catalina has a new security setting for this?
Several applications (GIMP for example) are not working also (they can't access "special" folders like: ~/Desktop, ~/Documents and ~/Downloads, but other locations seem to work OK). I believe this is a "complementary feature" bestowed by the newly-released Catalina.
I'm in pretty much the same boat as you. The exception being I'm using mamp 4.5.
I'm yet to find a solution however I can help you to see the mail log.
in terminal you can use:
log stream --predicate '(process == "smtpd") || (process == "smtp") || (process == "master")' -info
Using smarthost with the default mamp /etc/postfix/main.cf I keep getting: