Postfix email delivery fails with "warning - mail_queue_enter: create file maildrop/xx.xx: No space left on device"

Issue

• Postfix email delivery is failing due to the following warning message, despite sufficient free space on the /var file system.

postfix/postdrop[21509]: warning: mail_queue_enter: create file maildrop/293443.21509: No space left on device
postfix/postdrop[97310]: warning: mail_queue_enter: create file maildrop/859920.97310: No space left on device
postfix/postdrop[19961]: warning: mail_queue_enter: create file maildrop/589037.19961: No space left on device
postfix/postdrop[68922]: warning: mail_queue_enter: create file maildrop/970648.68922: No space left on device
postfix/postdrop[97468]: warning: mail_queue_enter: create file maildrop/740232.97468: No space left on device

Disk space usage information:

# df -l /var
Filesystem                               1K-blocks    Used Available Use% Mounted on
/dev/mapper/rootvg-var                     3997376 1392940   2378340  37% /var