Indico.emails Could not send email

Dear Community,
I have a fresh installation of indico 3 and indico.log show me this entry:
indico.emails Could not send email “[Indico] Verify your email” (attempt 1/10); retry in 30s [[Errno 111] Connection refused]

As in previous installation I configurated paramenters in this way:

SMTP host: localhost
SMTP port: 25
If your SMTP server requires authentication, enter the username now.
SMTP username:
SMTP connection failed: [Errno 111] Connection refused

I installed indico 3 with nginx and postgres 13 on Centos 7.9

Can someone point me to a possible solution?
Thank you all

I’m sorry,
my fault. I uninstalled postfix. Reinstalled and it works.