Steps to reproduce:

• Setup media type slack if upgrading from previous versions with the official documention: https://git.zabbix.com/projects/ZBX/repos/zabbix/browse/templates/media/slack?at=refs%2Fheads%2Frelease%2F5.0
• Verify on the Zabbix server, that there is no CLOSE_WAIT socket:

root@zabbix:/home/steffen# ss -ano | grep CLOSE-WAIT
root@zabbix:/home/steffen# 

• Create a new host with an unassigned IP address within your network and add the Template  Template Module ICMP Ping
• Wait __ a few minutes, until you receive the alert in Slack
• Check back for CLOSE_WAIT sockets on the Zabbix server:

root@zabbix:/home/steffen# ss -ano | grep CLOSE-WAIT
tcp   CLOSE-WAIT 40     0                                            10.10.20.8:47818                  3.123.248.34:443                                         
root@zabbix:/home/steffen# 

• Create another host (same procedure as before, with another unassigned IP) - or provoke an error otherwise of course.
• Wait again for the alert to show up in Slack
• Check one more time for CLOSE_WAIT sockets

root@zabbix:/home/steffen# ss -ano | grep CLOSE-WAIT
tcp   CLOSE-WAIT 40     0                                            10.10.20.8:59914                  3.123.248.34:443                                         
tcp   CLOSE-WAIT 40     0                                            10.10.20.8:47818                  3.123.248.34:443                                         
root@zabbix:/home/steffen# 

• Restart zabbix-server to verify, that CLOSE_WAIT sockets are gone, after the application exits

root@zabbix:/home/steffen# systemctl restart zabbix-server
root@zabbix:/home/steffen# ss -ano | grep CLOSE-WAIT
root@zabbix:/home/steffen# 

Result:

With every new alert a new CLOSE_WAIT socket will spawn and the server will eventually run out of open ports.
Expected:
No leaking sockets/CLOSE_WAIT sockets

Initially I "reported" the issue back in the beginning of 2020 [here|https://www.zabbix.com/forum/zabbix-troubleshooting-and-problems/394351-zabbix-4-4-5-slack-media-type-tcp-close-wait]and here.

I guess nobody is monitoring for CLOSE_WAIT sockets or is not making use of the webhooks.

BTW: The same can be reproduced with Discord as media type.