While sending emails using SquirrelMail, I was getting following error message;

ERROR: Could not append message to INBOX.Sent.
Server responded: [ALERT] Cannot create message – no write permission or out of disk space.

ERROR: Could not append message to INBOX.Sent.
Server responded: Error in IMAP command received by server.

ERROR: Connection dropped by IMAP server.
Query: LOGOUT

After a long investigation, I found a solution for this issue.
I have created tmp directory in /home/cPanel-Username/mail/Domain-Name/xyz/.Sent folder and issue get resolved.

Note:-
1 :: cPanel-Username is username of cPanel account
2 :: Domain-Name is the domain on which email address is created
3 :: xyz is a inital of email address

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1. If you are getting this error while accessing webmail.

ERROR: Could not complete request.
Query: SELECT “INBOX”
Reason Given: Unable to open this mailbox.

It means that there is some an issue while accessing email accounts via webmail. To resolve the issue, create the following folder at its loacation and assign the correct permission. You can do it with the help of following commands.

#cd /home/UserName/mail/Domainname.com/emailIDUsername/
#mkdir new; mkdir cur; mkdir tmp
#chown username.username*

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