Undelivered or blocked email (bounce): what it means and how to fix it

An undelivered or bounce message (often titled “Mail delivery failed”, “Undelivered Mail Returned to Sender”, or “Delivery Status Notification”) means your email was rejected or could not be delivered – by the recipient’s mail system or, for outgoing mail, by the filter on the GARMTECH server.

To fix it quickly, focus on the status code and the diagnostic message inside the bounce.

1) Identify whether it is a permanent or temporary failure

• 5.x.x – permanent failure (will not deliver until something changes).
• 4.x.x – temporary failure (often retries succeed later).

2) Common bounce reasons and what they mean

5.1.1 / “User unknown”

• The recipient address does not exist.
• Fix: verify spelling, confirm the mailbox exists, or contact the recipient via another channel.

5.2.2 / “Mailbox full”

• The recipient mailbox is out of storage/quota.
• Fix: ask the recipient to free space or increase quota; resend later.

5.7.1 / “Rejected”, “Blocked”, “Spam policy”

• The email was rejected due to policy or spam filtering – by the recipient server or by the outgoing filter on the GARMTECH side.
• Fix: use authenticated SMTP, avoid spam-like content, and go through the outgoing filter causes below – they apply in both cases.

4.4.x / “Timeout”, “Connection refused”, “Try again later”

• The recipient mail server was temporarily unavailable.
• Fix: wait and retry; this usually resolves automatically.

3) Blocked by the outgoing mail filter

All mail sent through GARMTECH servers passes an outgoing filter. It protects the sending reputation of the server and of your domain: if spam leaves the server, all customers’ mail starts landing in Spam folders or being rejected. Blocks are almost always triggered by one of these causes:

A compromised mailbox is sending spam

The most frequent cause. Signs: bounces for messages you never wrote, complaints from recipients, unusually high sent volume. Immediately change the mailbox password and scan the devices that use this mailbox for malware – see My email account is sending spam: secure GARMTECH Business Email.

Mass mailing / newsletters

Hosting and Business Email are meant for normal correspondence, not bulk campaigns. Large mailings quickly trigger rate limits and spam scoring – use a dedicated newsletter service (with its own SPF/DKIM) for campaigns.

Content that looks like spam

Shortened links, many images with little text, spam-typical wording, or a link to a hacked or blacklisted site in your signature can all trigger the filter. Review the message content and any links it contains.

Missing SPF/DKIM/DMARC

Without correct DNS authentication records, receiving servers and filters distrust your mail. Check: Set up SPF, DKIM, and DMARC for your domain.

A website form or script is sending the mail

If the block concerns mail sent by your website (contact form, shop), see Website contact form not sending emails and use authenticated SMTP: Send emails from your website via SMTP.

4) How to read a bounce (what to copy)

In the bounce message, look for lines like:

• Status: 5.7.1
• Diagnostic-Code: explains why the remote server refused it
• Final-Recipient: the exact address that failed

5) Checklist for sending from GARMTECH email

• Send through SMTP‑SSL (port 465) with authentication.
• Use your service server hostname as the mail server name (as shown in My.GARMTECH).
• Ensure DNS has valid SPF, DKIM, and DMARC records for your domain.
• Use strong, unique mailbox passwords (enable 2FA where available) and keep your website and CMS updated so they cannot be abused for sending spam.
• If you send a lot of mail, increase gradually and keep bounce rates low.

6) What to send to support

If the cause is not obvious or a block persists after you fixed it, open a ticket and include the full bounce message, including the error text and codes. It contains the exact reason and lets us request an unblock quickly. Do not delete the bounce email.

7) If you receive bounces for inbound mail

If someone tells you they cannot email you, the bounce is on their side. Ask them to forward you the bounce text – it will show whether:

• your domain has wrong MX records (mail goes elsewhere),
• your mailbox does not exist,
• the sender is blocked by spam policy.

Tip: You can always check your mailbox directly in GARMTECH.Email to confirm it receives mail.