HELO/EHLO
HELO and EHLO are the commands a sending server uses to identify itself at the start of an SMTP conversation.
HELO (Hello) and EHLO (Extended Hello) are the first commands sent by a client or sending server to start an email transmission session. They are effectively saying, "Hi, I am [server-name], and I want to send email."
EHLO is the modern version that asks the receiving server which "Extended SMTP" (ESMTP) features it supports, like encryption (STARTTLS) or large file sizes. If the server doesn't understand EHLO, the sender falls back to the older HELO.
Receiving servers check the hostname provided in the HELO/EHLO command. If a server claims to be google.com but its IP address belongs to a residential ISP, it will be flagged as suspicious.
Related Terms
SMTP
SMTP (Simple Mail Transfer Protocol) is the standard way email servers send messages to each other. It handles the handoff from your email tool to the recipient's mail server so messages can land in the inbox.
Learn more →Dedicated Server(Dedicated IP)
A dedicated server is a private email server with its own IP address that only your company uses to send email. It gives you direct control over your sender reputation and delivery results.
Learn more →SMTP Banner(Service banner)
The SMTP banner is the initial text greeting a mail server sends when a connection is first established.
Learn more →Shared Server(Shared IP)
A shared server is an email server and IP address that many companies use to send their emails. Your messages go out from the same place as other senders, so you share the same reputation.
Learn more →