Is it possible to send and receive an email from an IP address instead from a domain?

Usually an email has a domain name on the right side of the @, so you can identify an organization or a company. This domain is in fact nothing other than a "name" or an "alias" for an IP address, resolved by the name server.

I think this could be used for example for the Internet of Things, because there are many more possibilities compared to POST and GET like "many to one" or "one to many".

Is there a way to send and receive emails directly to and from an IP address, as [email protected] for example?

For emails, a domain is not merely an alias or human readable form for an IP address: mail exchanger MX records exists to specify mail servers responsible for accepting email messages on behalf of a recipient's domain. There could be several servers accepting mail for the domain, and they are not necessarily on the same IP that's in the A record for the domain. A mail system can have several servers: incoming servers might be separated from outgoing servers and mail storage servers etc. The A record is only used when there's no MX records specified for the hostname.

However, there's no (other) limit in email address format that you could not send emails directly to <[email protected]> or even <user@[198.51.100.10]> (IP with the square brackets). If there was a mailserver that accepts email using the plain hostname or even IP address, it would do. But what you are suggesting doesn't work globally in practice:

• Most email systems have several domains and need to handle email separately for them all. The username itself may not have been bound to any actual mailbox as <[email protected]> might be a different person than <[email protected]>
• While this was common couple of decades ago, fighting spam has made things more complicated and accepting email has strict limits.
• The usage of SMTP port 25 is very limited on consumer grade internet connections due to abuse (spambots). There isn't really that much use of SMTP for IoT devices.

Many SMTP servers (e.g. sendmail) handle user@[aaa.bbb.ccc.ddd] email addresses BUT

1. Some SMTP server do not handle/recognize it
   They may refuse to accept such sender address or be unable to send to such address.
2. Such addresses may cause problems with some anti-spam software

RFC-5322 : 3.4.1. Addr-Spec Specification

Wikipedia: Email address - domain part

… In addition, the domain may be an IP address literal, surrounded by square brackets [], such as jsmith@[192.168.2.1] or jsmith@[IPv6:2001:db8::1], although this is rarely seen except in email spam. …