In other words, RFC 5322 says that either a domain name form or a domain literal form may be used to describe the domain portion of an email address. In the domain- literal form, the domain is interpreted as the literal Internet address of the particular host. In the dot-atom form, this is interpreted as an Internet domain name (either a hostname or a mail exchanger name) as described in, , and. The domain portion identifies the point to which the mail is delivered. In the email address specification section of RFC 4532, we see where the specification mentions the use of a domain-literal form, i.e. Email addresses with IP addresses often get flagged as spam.Įmail messages are transmitted using the Simple Mail Transfer Protocol (SMTP), which is defined by the Request for Comments (RFC) 5321, 5322 and various extensions.For a mail server that hosts more than one domain, the FQDN in the email address is necessary to identify which domain group the email user belongs to.By default, it is not uncommon for many mail servers to not accept email addresses without a ‘fully qualified domain name’ (FQDN).The Simple Mail Transfer Protocol (SMTP) does allow an IP address to be used instead of a domain name under special circumstances when encapsulated in brackets, such as our previous example of However, here are some common reasons why doing so may end up with the email message being bounced back and/or not making it to the intended recipient.

The short answer is technically yes, but really no. Some of your contact email addresses may contain an IP address, for example, rather than a domain name, such as Can you use these email addresses for mailing purposes?

Helo for atomic mail verifier