zimbraMtaAuthURL:
https://myhost.com:443/service/soap/
This is wrong (and probably what's killing the mta) - this is a known bug - basically, you're authing against 443, and your server is only listening on 80 (zimbraMailMode=http). To fix this:
zmprov ms myhost.com zimbraMtaAuthHost myhost.com
(Which is what it's already set to) will refresh the URL based on the mail mode.
I don't think this is what's killing tomcat, but it could be...