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# How to fix warming emails not being delivered (Custom SMTP)

# Why are my warm-up emails not being delivered (Custom SMTP)

If you're seeing a warning like:

“All warm-up emails from your address aren’t being delivered. Check your SMTP setup.”

… this means that MailReach tried to send warm-up emails via your Custom SMTP configuration, but they never reached any recipient inbox — not even spam folders.

## What does this mean?

All your warm-up emails are marked as "missing", which typically indicates one of the following:

* Your SMTP provider is silently blocking or dropping emails
* Your SMTP server is misconfigured
* Authentication settings (login/password, ports, encryption) are incorrect
* There are sending limits, IP blocks, or anti-spam filters stopping the delivery

In short: the problem is on your side (SMTP setup) or with your email provider.

MailReach can’t “see” exactly where the problem is — we can only detect that the emails aren’t reaching any inbox.

## What you should check

We recommend verifying the following points in your Custom SMTP setup:

**SMTP credentials & server details**
* Are the hostname, port, and encryption (SSL/TLS) settings correct?
* Are the credentials (username/password) still valid?

**Look for bounce messages or SMTP errors**
– If your SMTP server returns **delivery errors or bounce messages**, they usually contain a **code or explanation** (e.g. *“550 5.4.6 Unusual sending activity”*).
– These clues can help you or your provider identify exactly what's wrong.

**Authentication & sending permissions**
* Does the SMTP server allow sending from the address you've connected?
* Is authentication (login) required and correctly configured?

**Provider-side limitations**
* Are there daily sending limits? Quotas reached?
* Is your account or IP flagged or blocked by the provider?

**Technical settings**
Are SPF, DKIM, and DMARC records properly set up?
→ You can check this under the “Checks” tab in MailReach.


## Common reasons this issue may happen

Here are a few real examples of known cases:

* **Provider silently drops messages due to reputation or content**
Some providers have spam filters that block delivery without bounce-back.
* **Expired or incorrect SMTP credentials**
A password change or permission update can silently break the connection.
* **You’re using an alias not authorized for sending**
Some SMTP servers only allow sending from certain verified addresses.
* **You hit a sending limit (daily/hourly)**
Once the limit is hit, emails may be silently dropped or delayed.
* **Zoho Mail blocks SMTP sending due to “unusual activity”**
You might see the error `550 5.4.6 Unusual sending activity detected`.
→ [Zoho’s usage policy](https://www.zoho.com/mail/help/usage-policy.html)

🧠 *We'll keep adding to this list as we discover new causes.*

## How to test

To confirm that your SMTP is working correctly:

1. Try sending a test email using your SMTP to a mailbox you own and see if this test email lands in the mailbox.
2. Reach out to your provider's support team and ask: "Are emails sent via SMTP from this account being delivered? Are there any restrictions or blocks?"


## Still stuck?

👉 Reach out to our support team with:

* The email address affected
* A screenshot of your SMTP settings (with sensitive info blurred if needed)
* Any test results you’ve run

We’ll do our best to point you in the right direction!