Port problems, how to solve?

Question

iptables

Opened port 2500
-A INPUT -p tcp -m tcp --dport 2500 -j ACCEPT
Until today everything worked perfectly.

I started getting the error
Timed out, status = ETIMEDOUT while connecting from you-it.ru (0.0.0.0) to [127.0.0.1] (127.0.0.1)

Checking the port

lsof -i :2500
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
pmtad 896 pmta 37u IPv6 3671916929 0t0 TCP *:rtsserv (LISTEN)

It ​​turns out that he only wants to communicate with ipv6?
How to do with ipv4?