YOUR MAIL SERVER REJECTS YOUR EMAIL SMTP\SEND
It is up to your mail host to decide the rules of outgoing mails will be and how to reduce domains from getting marked as spammers.
Spammers are out there, and they are active in sending billions of spammails.
Radicati Group’s estimate for 2015 was 205 billion emails per day and percentage of email that is spam: 49.7 percent; Percentage of emails that have a malicious attachment: 2.3 percent.
There are several ways that email servers use and new standards such as DMARC and SPF are becoming a standard.
This makes providers to easyly tell if a mail is legitimate or SPAM.
HELO is such a standard and helps spamdetection in finding out who the mail was sent from.
The server checks out the format of the HELO and although this can be disabled, it is highly advised to set this at qualified domain name.
Accepted HELO:
HELO ourbusiness.company.com
The following bad example(s) will get rejected:
HELO standard rejection reasons:
HELO localhost
HELO localhost.localdomain
HELO hostnameonly
HELO internal ip (10.0.0.40 so on)
HELO 192.168.1.1 (just an IP)
HELO
HELO .com (period)
HELO mail..com
HELO @(&$ (characters not normally allowed in domain names)
Here is an example of the code EXIM4 uses to check HELO
Helo name contains a ip address
acl_check_mail:
deny condition = ${if eq{$sender_helo_name}{}}
message = HELO required before MAIL
drop message = Helo name contains a ip address (HELO was $sender_helo_name) and not is valid
condition = ${if match{$sender_helo_name}{\N((\d{1,3}\d{1,3}\d{1,3}\d{1,3})|({8})|({8}))\N}{yes}{no}}
condition = ${if match {${lookup dnsdb{>: defer_never,ptr=$sender_host_address}}\}{$sender_helo_name}{no}{yes}}
delay = 45s
drop condition = ${if isip{$sender_helo_name}}
message = Access denied – Invalid HELO name (See RFC2821 4.1.3)
drop condition = ${if eq{}{$sender_helo_name}}
message = $interface_address is _my_ address
accept
HOW TO FIX THUNDERBIRD GETTING REJECTED
So now that we understand how and what HELO is, the message: «Helo name contains a ip address (HELO was 10.0.0.110) and not is valid» makes more sense.
This is because Thunderbird mail sometimes uses your ip as hostname, depending on your network or router setup.
We will need to change the HELO identification to localhost so you can identify correctly to your mailserver that is a little spamscared!
STEPS TO FIX
First off, fire up your Thunderbird and select TOOLS -> OPTIONS
Now select Advanced -> General -> Config Editor
In the seachbar type:
mail.smtpserver.default.hello_argument
then set the value to:
localhost
This should take care of your dreaded problem with noone liking your IP address!
Until next time!
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