Email Not Receiving or Not Being Delivered
Step-by-Step Troubleshooting Guide

Email delivery problems — not receiving emails or emails not getting through — are among the most frustrating issues for business owners. This guide walks you through a systematic diagnosis, from DNS configuration to blacklist checks, with actionable solutions at each step.

How Email Delivery Works

Understanding the email delivery path helps you pinpoint where things go wrong. When someone sends you an email, the process is:

1. The sender's mail client submits the message via SMTP to their outbound mail server
2. The sending server queries DNS for the MX record of the recipient's domain
3. It connects to the recipient's mail server listed in the MX record
4. The receiving server checks SPF, DKIM, DMARC, and spam scoring
5. Pass → delivered to mailbox | Fail → rejected or quarantined

Check MX Record

The MX (Mail Exchange) Record tells the internet which mail server handles email for your domain. If it's wrong or hasn't propagated, no email will reach you.

How to Check Your MX Record

nslookup -type=MX yourdomain.com
# or on Linux/macOS
dig MX yourdomain.com

A correct result shows your mail server's hostname, for example:

yourdomain.com  mail exchanger = 10 mail.yourdomain.com

Symptom	MX Cause	Fix
NXDOMAIN / No MX record	No MX record exists	Add MX record in your DNS panel
MX points to wrong server	Changed MX but old cache remains	Wait for TTL to expire (usually 24h) or reduce TTL first
Correct MX but still propagating	Just changed nameservers	Wait 24–72h, check propagation at whatsmydns.net
Multiple MX with same priority	Unintended load balancing	Set different priorities (10, 20)

Check Disk Quota

Disk quota is the storage limit for your mailbox. When it's full, the mail server rejects new incoming messages with bounce code 452 4.2.2 Mailbox full, and senders receive a bounce notification.

Check Quota via DirectAdmin

1. Login to DirectAdmin > E-Mail Manager > E-Mail Accounts
2. Check the Quota Used column for each email account
3. If at or near 100%, take action immediately

Fixing a Full Mailbox

• Delete old emails from Inbox, Sent, Trash, and Spam — especially those with large attachments
• Archive old emails to your local machine using an email client (Thunderbird, Outlook)
• Expand mailbox quota in DirectAdmin (if your hosting plan has space remaining)
• Upgrade your hosting plan if more storage is needed long-term

Spam Filter and Blacklist

Spam filters act as the first line of defense for incoming mail. Both the receiving server (yours) and the sending server's IP reputation affect deliverability.

Types of Spam Filters

Type	How It Works	How to Fix
IP Blacklist (DNSBL)	Checks sender IP against blacklists	Submit delisting request to DNSBL providers
Content Filter	Analyzes content, subject, and keywords	Avoid spam trigger words like "Free", "Click here"
Reputation Score	Domain/IP sending reputation score	Warm up new IP gradually, send engagement emails
SpamAssassin Score	Cumulative score >5 = spam	Test via mail-tester.com before bulk sends

Check for IP Blacklisting

First find your mail server's IP address (from email headers or DirectAdmin), then check these tools:

• MXToolbox Blacklist Check: mxtoolbox.com/blacklists.aspx
• MultiRBL: multirbl.valli.org
• Spamhaus: check.spamhaus.org

SPF, DKIM, and DMARC

These three email authentication standards work together to verify that email comes from legitimate sources. Missing or misconfigured records result in rejection or spam folder delivery.

SPF (Sender Policy Framework)

SPF is a TXT DNS record that specifies which IP addresses or mail servers are authorized to send email on behalf of your domain.

# Example SPF Record
v=spf1 mx a:mail.yourdomain.com ~all

# Meaning:
# v=spf1         = SPF version 1
# mx             = authorize the domain's MX servers
# a:mail.yourd.. = authorize the IP of mail.yourdomain.com
# ~all           = everything else = SoftFail (use ~all first, switch to -all when confident)

DKIM (DomainKeys Identified Mail)

DKIM adds a cryptographic signature to outgoing mail. Recipients verify it against the public key in DNS to confirm the message wasn't altered in transit.

• Configure DKIM via DirectAdmin > Email Manager > DKIM Keys
• Copy the public key to your DNS panel as a TXT record at default._domainkey.yourdomain.com
• Verify with: dig TXT default._domainkey.yourdomain.com

DMARC (Domain-based Message Authentication)

DMARC defines the policy: what to do when email fails SPF or DKIM — none (report only), quarantine (send to spam), or reject (block).

# Example DMARC Record
_dmarc.yourdomain.com TXT "v=DMARC1; p=quarantine; rua=mailto:[email protected]"

Record	DNS Location	Check Tool
SPF	yourdomain.com (TXT)	mxtoolbox.com/spf.aspx
DKIM	default._domainkey.yourdomain.com (TXT)	dkimvalidator.com
DMARC	_dmarc.yourdomain.com (TXT)	mxtoolbox.com/dmarc.aspx

Reading Mail Logs

Mail logs record every event that happens with your mail server, giving you the most accurate information about exactly where an email got lost.

Access Mail Logs via DirectAdmin

1. Login to DirectAdmin as Reseller or Admin
2. Go to System Info & Files > Log Viewer
3. Select Exim Mail Log (/var/log/exim/mainlog)
4. Search by email address or domain name

Interpreting Key Log Entries

# Successful delivery
2026-08-10 10:15:32 [1234] => [email protected] R=dnslookup T=remote_smtp H=mail.example.com [1.2.3.4] ... "250 OK"

# Rejected by destination
2026-08-10 10:15:32 [1234] ** [email protected]: SMTP error from remote mail server after RCPT TO
550 5.7.1 Message rejected as spam by Content Filtering

# Quota exceeded
2026-08-10 10:15:32 [1234] [email protected]: Mailbox disk quota exceeded

Outbound Email Issues

Beyond not receiving email, you may also have trouble sending. Messages might queue up or bounce back to you.

Common Outbound Failure Causes

• Port 25 blocked: ISPs and cloud providers block port 25 to prevent spam — use an SMTP relay service (SendGrid, Amazon SES) instead
• Authentication failure: Wrong SMTP username or password — verify in your email client settings
• Expired SSL/TLS Certificate: Certificate expired or self-signed — check via DirectAdmin > SSL Certificates
• Rate limiting: Sending too many emails per hour — contact support to increase limits

Port	Protocol	Use Case
25	SMTP (unencrypted)	Server-to-server only; usually blocked by ISPs
587	SMTP STARTTLS	Submission port — recommended for email clients
465	SMTP SSL/TLS	Legacy SSL — still works but 587 is preferred
993	IMAP SSL	Receive email via IMAP with SSL
995	POP3 SSL	Receive email via POP3 with SSL

Complete Diagnostic Checklist

Work through this checklist systematically to find the root cause:

Frequently Asked Questions

Summary

Email delivery problems often stem from multiple contributing factors simultaneously. Systematic diagnosis using the checklist finds the root cause much faster than guessing. Start with DNS (MX, SPF, DKIM, DMARC), move to quota, then check mail logs — in most cases you'll find the issue within the first 4–5 steps.