MSG="From: a@gmail.com
To: Receiver
Subject: Test"

echo "$MSG" | curl --url 'smtps://smtp.gmail.com:465' --ssl-reqd
--mail-from "a@gmail.com" --mail-rcpt "receiver@gmail.com"
--upload-file - --user "a@gmail.com:password" --insecure

EXISTS="$(curl --insecure
--user "a@gmail.com:password"
--url 'imaps://imap.gmail.com:993/'
--request "EXAMINE INBOX" | grep "EXISTS" | grep -oP 'd*' | head -n1 )"

echo "$EXISTS"

for ((i=$EXISTS;i!=$EXISTS-5;i--)); do
   SUBJECT="$(curl --insecure -u "a@gmail.com:password"
   --url "imaps://imap.gmail.com:993/INBOX;UID=$i" |
   grep "Subject: " | head -n1 )"

   echo "$SUBJECT"
done