While you're working on figuring out how to send an email from your gmail address I took a look at your storage usage:
Backups 0 MB
Emails 0 MB
Files 1001.69 MB
Trash 0 MB
Logs 13.74 MB
PSQL 0 MB
MariaDB 36.82 MB
Total 1052.25 MB
260M /home/gentillenoir075.helioho.st/httpdocs
12K /home/gentillenoir075.helioho.st/.ssh
77M /home/gentillenoir075.helioho.st/git
24K /home/gentillenoir075.helioho.st/.nodenv
62M /home/gentillenoir075.helioho.st/.npm
8.0K /home/gentillenoir075.helioho.st/private
251M /home/gentillenoir075.helioho.st/sitex.quevvy.com
291M /home/gentillenoir075.helioho.st/quevvy.com
0 /home/gentillenoir075.helioho.st/tmp
0 /home/gentillenoir075.helioho.st/var
29M /home/gentillenoir075.helioho.st/usr
12K /home/gentillenoir075.helioho.st/etc
0 /home/gentillenoir075.helioho.st/dev
16K /home/gentillenoir075.helioho.st/files_docker
4.0K /home/gentillenoir075.helioho.st/.config
35M /home/gentillenoir075.helioho.st/.cache
4.0K /home/gentillenoir075.helioho.st/.local
It seems like the problem is you asked us to remove the sitex.quevvy.com domain, but you never deleted the files, and then you put all the same files into the quevvy.com domain thereby doubling the usage of that site. After deleting that duplicate sitex.quevvy.com directory for you your storage usage is at 802 MB out of 1000 MB.
Now that you're under the 1000 MB limit you should be able to login again and your 503 errors are gone. If you need more than 1000 MB storage you can increase your limit at https://heliohost.org/dashboard/storage/ If you're no longer able to send emails from your gmail account for some reason you could always change your email address in Plesk so we can accept reset requests from this email address too.
Let us know if you need help with anything else.