Due to the lack of the disk space on partitions like / or /var, it's sometimes necessary to move the /var/vmail folder to a larger partition which has more free space and mostly to the /home partition.
You can check the list of your partitions with this command:
Before moving the emails you should first check the actual usage of /var/vmail with this command
du -hs /var/vmail
Step 1: We advise you stop postfix and dovecot during this process
systemctl stop postfix dovecot
Step 2: copy the vmail folder to the new location
rsync -av /var/vmail/ /home/vmail/
The Above command will copy the folder vmail to /home, so we will have /home/vmail. All permissions will be maintained as well.
Step 3: Backup /var/vmail folder
mv /var/vmail /var/vamil.orig
Step 4: create a symlink from the new location to old location
ln -s /home/vmail /var/vmail
Step 5: start postfix and dovecot
systemctl start postfix dovecot
You can then test send and receipt of emails. If all is ok, then you can delete the /var/vmail.orig folder to make the space available.
Correct permissions are required (edit if you use different location)
chmod 770 /var/vmail
chown vmail.mail /var/vmail
MAIL DISK QUOTA (postfix vmail)
Please note that if you want quota to work for mail then it needs to be on the same partition as user home files.
If you have a custom partition for /home then you will need to have /var/vmail moved per instructions to /home/vmail