POSTFIX Error: 421 4.7.0 Try again later, closing connection. (EHLO)

Question

I setting main.cf in postfix on Linux SUSE like this

inet_interfaces = localhost
inet_protocols = ipv4

masquerade_domains =
masquerade_exceptions = root
mydestination = $myhostname, localhost.$mydomain
myhostname = localhost
mynetworks_style = subnet
relayhost=[smtp-relay.gmail.com]:25

smtpd_delay_reject = yes
smtpd_helo_required = no

smtpd_client_restrictions =

smtpd_helo_restrictions =

smtp_sasl_auth_enable = no
smtp_sasl_security_options =
smtp_sasl_password_maps =
smtpd_sasl_auth_enable = no

smtp_use_tls = no

I tried to telnet smtp-relay.gmail.com 25 and it's working

Anyway, when I tried to send email with postfix in server I got the issue.

root@localhost
(host smtp-relay.gmail.com[ipv4] refused to talk to me: 421 4.7.0 Try again later, closing connection. (EHLO)

Solution

Looking at the official Google documentation looks like a "ratelimit" on their side:

 421, "4.7.0", Try again later, closing connection. This usually indicates a Denial of Service (DoS) for the SMTP relay at the HELO stage.

How many mails per minute are you sending? By experience, usually Gmail accepts 50/100 mail/minute tops.

EDIT as per comment

Well, looks like the same error appears with a wrong HELO/HELO (as I first suspected).

I just tried:

$> telnet smtp-relay.gmail.com 25
Trying 108.177.15.28...
Connected to gmail-smtp-relay.l.google.com.
Escape character is '^]'.
220 smtp-relay.gmail.com ESMTP b8-v6sm74445wrr.1 - gsmtp
helo localhost
421 4.7.0 Try again later, closing connection. (EHLO) b8-v6sm74445wrr.1 - gsmtp
Connection closed by foreign host.

So it's definitively your EHLO string.

You have myhostname = localhost in your main.cf file, you should change it with myhostname = [your server fqdn], i.e. you should have a Fully qualified domain name for your server, complete with correct DNS/rDNS entries.

Comments

[user9111600]

I just sent only 1 email per minute or I can say 1 email per hour.

[Esa Jokinen]

Using temporary error code on a permanent error is not very wise from Google.

[user9111600]

@Mr Shunz, I still don't have FQDN just now maybe the process will finish on the next week, so can I use ip adress instead?

[Daniele Santi]

@user9111600 I just tried and it seems the error does not appear when using helo IP.ADD.RE.SS. Give it a try!

[user9111600]

@ Mr Shunz, I just try with your suggestion but it still showing.. root@localhost (delivery temporarily suspended: host smtp-relay.gmail.com[74.125.24.28] refused to talk to me: 421 4.7.0 Try again later, closing connection. (EHLO)

[user9111600]

It showing error already: postfix: warning: valid_hostname: numeric hostname: 110.49.142.77 maybe I cannot use ip to being hostname.

[Daniele Santi]

@user9111600 you should definitively get a FQDN then.