SMTP
SMTP is the protocol that moves outgoing mail from a sender to the destination server. The exchange is plain text commands: the client greets, names a sender and a recipient, then hands over the body. SMTP only sends. Incoming mail is read through another protocol, IMAP and POP3.
The actual SMTP conversation
EHLO mail.example.com
MAIL FROM:<[email protected]>
RCPT TO:<[email protected]>
DATA
EHLO opens the session and lists what each side supports. MAIL FROM sets the sender, RCPT TO sets a recipient and can be repeated for several addresses, and DATA ends the command phase and starts the body. If RCPT TO already returns an error, the message will never be delivered no matter how strong your SPF record is. A multi-line reply such as 250-AUTH lists the authentication mechanisms the server supports.
Ports and TLS modes
Port 25 is the original SMTP port, now rarely used by clients because many providers block it. Port 465 uses implicit TLS, encrypting from the first byte. Port 587 is the standard submission port for authenticated sending with STARTTLS. Port 2525 is a common fallback when 587 is blocked. For normal mail clients, try 587 with STARTTLS first. For mail moving between servers, port 25 is still the norm, so the block targets clients rather than MTA relays.
Why port 25 gets blocked
A lot of new hosting blocks outbound port 25 to cut down spam from hijacked accounts. This limit varies by provider and even by plan, so there is no single answer. Check your plan documentation or panel, and ask support whether outbound 25 is actually open. If it is closed, you can still send over 587 or 465, or route through a third-party sending service.
Accepted is not delivered
This is the costly trap. A receiving server replies 250 when it accepts the message, but that does not promise an inbox landing. The real outcome depends on domain reputation and the matching DNS records, mainly SPF, DKIM, and DMARC. The two signals to read are inbox-versus-spam test results and bounce codes. A hard 5xx bounce means a permanent rejection, a 4xx bounce means a temporary one. Email deliverability is the measure that matters, not the sent status. The 250 code only says the receiver agreed to store the message, nothing about an inbox landing.
FAQ
Does SMTP help receive email?
No. SMTP is for outgoing mail only. Incoming mail comes through IMAP or POP3, or is read in webmail.
Does WordPress need a custom SMTP setup?
Usually yes. WordPress sends through the PHP mail() function by default, which receiving servers often treat as spam. Point an SMTP plugin at a proper server so notifications and password resets actually arrive.
My mail always lands in spam, where do I start?
Check SPF and DKIM first, then confirm the sending IP is not on a blocklist. Without both, even legitimate mail gets filed into spam.
Disclaimer: Hosting Wiki articles are prepared for educational and reference purposes. Hosting technology keeps evolving, so some technical details may change over time.