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SMTP deliveryPostfix/qmail and port 25
Halkali merkez neighborhood fatih st ozgur apt no 46 , Kucukcekmece , Istanbul , 34303 , TR
Plesk mail issues are divided into separate layers for sending, receiving, authentication, and delivery. Postfix or qmail, Dovecot, DNS records, port 25 output, mail queue, spam block due to source, and mailbox quota should be diagnosed separately.
status=deferred (connect to mx.example.net[203.0.113.10]:25: Connection timed out)
SASL authentication failed
Mailbox full
Relay access denied
Host or domain name not foundThe process of a message leaving the Plesk server, reaching the target server, being accepted, and appearing in the recipient's mailbox are separate stages. The phrase "mail is not being sent" should first be substantiated with queue and log.
If the message is deferred in the queue, there may be a connection issue to the counter server, DNS resolution, greylisting, or a temporary delivery rule issue.
If port 25 is blocked by the data center, direct external SMTP delivery from the server cannot be made. A smarthost/relay or provider port opening process may be required.
If mail is coming but not showing in webmail, check mailbox quota, Dovecot, folder permissions, or filter rules.
In addition to SPF, DKIM, DMARC, PTR/rDNS, IP reputation, and message content, SPF, DKIM, DMARC, PTR/rDNS, IP reputation, and message content are also important for delivery to Gmail and Outlook.
Clearing the queue collectively does not solve the main issue and may lead to the loss of legitimate emails. The account that sent the most messages, the error cause, and the queue age should be analyzed first.
Search for the phrase you see in the email, browser, or SSH log. Each card includes meaning, probable cause, and safe initial action.
Meaning: Failed to connect to the SMTP port of the postfix facing server.
Possible cause: Port 25 block, remote firewall, route or destination server issue.
Meaning: The message has been temporarily undeliverable and has been held in the queue.
Possible cause: Timeout, DNS, 4xx response, greylisting, or remote quota.
Meaning: SMTP client username or password could not be verified.
Possible cause: Incorrect password, 465/587 encryption setting or account lock.
Meaning: The server has not granted unauthorized relay permission to the client.
Possible cause: Identity verification is not performed or the wrong SMTP server is being used.
Meaning: The recipient's mailbox or subscription disk quota is full.
Possible cause: Mailbox quota, disk/inode or large messages.
Meaning: The recipient's domain MX/A record could not be resolved.
Possible cause: DNS resolver issue, incorrect domain or temporary DNS failure.
Meaning: The counter-server message has been rejected due to IP or policy reasons.
Possible cause: Spam sending, bad PTR, blacklist or DMARC failure.
Meaning: IMAP/POP session could not be verified.
Possible cause: Incorrect password, mailbox malfunction, service or SSL setting.
No records matching this expression were found.
Commands are for root access. Collect only status and logs first; Do not change the permanent setting without seeing the reason.
systemctl status postfix dovecot --no-pager
systemctl status qmail --no-pager 2>/dev/nullDisplays the status of the installed MTA and IMAP services.
tail -n 200 /var/log/maillog 2>/dev/null || tail -n 200 /var/log/mail.logIt shows the reasons for submission, delivery, auth, and red.
postqueue -p
postqueue -p | tail -n 1Lists messages in the queue and the overall status.
postcat -q KUYRUK_IDDisplays the header and delivery error details of a specific queue message.
nc -vz gmail-smtp-in.l.google.com 25
openssl s_client -starttls smtp -connect localhost:25 -crlf </dev/nullTests external port 25 access and local SMTP TLS response.
dig +short MX example.com
dig +short TXT example.com
dig +short -x SUNUCU_IPMX shows MX, SPF-like TXT, and PTR/rDNS records.
plesk repair mail example.comInteractively checks domain mail settings and mailbox configuration.
First, determine the direction of the problem; then sequentially review the queue, logs, network, DNS identity, and account security layers.
Separate outgoing and incoming mail, webmail, and SMTP client tests.
Record the sender, recipient, and time of the test message, and follow the related queue ID in maillog.
Instead of checking the queue size, analyze the last delivery reason row of a message with postcat and maillog.
postqueue -pBy testing port 25 on multiple major providers' MX servers, local blockage and target problems can be separated.
The sender domain, HELO hostname, and rDNS must be compatible with each other; the DKIM signature must be verified.
If the account is in violation, change the password, clean the PHP spam script, and protect the legitimate messages in the queue.
Header authentication-results, PTR, IP reputation, content, and sending volume are examined.
MX records, port 25 inbound firewall, local mail service, and mailbox quota are checked.
Plesk domain must have local mail service disabled and MX records should only show the external provider.
The user, SASL account, or PHP script with the most sends is detected and isolated; the queue is not cleared blindly.
The client port, TLS type, SMTP AUTH, username, and certificate hostname are checked.
Remote SMTP connection timeout, DNS issue, temporary 4xx rejection, greylisting, or remote quota may delay delivery.
587 is for clients to send messages to the server. Delivery from the server to other MX servers usually requires port 25 or a smarthost should be used.
Linux Plesk uses Postfix by default; a qmail option may also be available. Commands vary depending on the installed MTA.
No. It strengthens authentication; IP reputation, content, volume, and user interaction also affect delivery.
The IP address is changed via a data center or server provider; it is not managed from the normal domain DNS panel.
Technically possible, but may cause legitimate message loss. First, spam and normal messages should be separated.
If the local mail service for the domain remains open, applications on the server may mistakenly deliver the message to the local mailbox. It should be configured to an external service.
By analyzing cPanel, WHM, CloudLinux, LiteSpeed, MariaDB, Exim and security layers together, we fix the root cause of the failure instead of just removing the service.