Error :- Connection timed out 110 Can't open SMTP stream

checking my smtp connections with

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netstat -a | grep smtp
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I like all of you have been having the same problem. Here's how I fixed it.

# Block outgoing SMTP except for root, exim and mailman (forces scripts/users
# to use the exim/sendmail binary instead of sockets access). This replaces the
# protection as WHM > Tweak Settings > SMTP Tweaks. This will block hosting
# clients from using your server as an SMTP relay

SMTP_BLOCK = 1

# If SMTP_BLOCK is enabled but you want to allow local connections to port 25
# on the server (e.g. for web scripts) then enable this option too

SMTP_ALLOWLOCAL = 1

I originally had SMTP_ALLOWLOCAL = 0 and SMTP_BLOCK set to 1. The notes in the config make mention of local script access.

Worked for me with SquirrelMail's conf set to useSendmail = false;
If you have:

SMTP_BLOCK = 1

then

SMTP_ALLOWLOCAL should also be set to "1"

If Getting The 110 Can't Open SMTP Error:

Do this:

Edit the following file, and change useSendmail to true, instead of false:

/usr/local/cpanel/base/3rdparty/squirrelmail/config/config.php

Save this, and close it, but you must do the following so that cpanel doesn't change useSendmail back to false:

chattr +ai /usr/local/cpanel/base/3rdparty/squirrelmail/config/config.php