- Plesk for Linux
The mailbox cannot be created via Plesk > Domains > example.com > Email Addresses > Create Email Address due to the following error:
PLESK_ERROR: ERR [util_exec] proc_close() failed ['/opt/psa/admin/bin/mailmng-core' '--add-mailname' '--domain-name=example.com' '--mailname=john.doe'] with exit code 
mailmng-core failed: Fatal error: boost::filesystem::filesystem_error(boost::filesystem::create_directory: Too many links: "/var/qmail/mailnames/example.com/john.doe"
The mailbox under a newly created subscription can be added without any issues.
The subdirectory cannot be created under the affected
# mkdir /var/qmail/mailnames/example.com/john.doe
mkdir: cannot create directory `john.doe': Too many links
The current number of sub-directories under the affected directory is 32000:
# ls -l /var/qmail/mailnames/example.com/ | wc -l
Reached sub-directories limit under the
On ext3 file-systems this limit is equal to 32000 sub-directories
This limitation on the OS level - Plesk cannot manage or influence it.
To resolve the issue one of the following solutions can be applied:
Remove non-required mailboxes under the
example.comsubscription via Plesk > Domains > example.com > Email Addresses > Remove.
Create a new subscription via Plesk > Subscriptions > Add Subscription and add a new mailbox under it via Plesk > Subscriptions > example2.com > Mail > Create Email Address.