$ nmap -Pn -p993 imap.gmail.com |& grep -q 'Host is up' && { ... }

And of course someday the printed text will change and I'll have to edit
my scripts again! Oh well. :-/

Host is up wouldn't be right - you need to parse to see if the port is listed as open or closed...

Something like:

nmap -Pn -p993 imap.gmail.com | awk '$1 ~ /993/ {print $2}' | grep open