Sending fails
SMTP connection test and sending error messages — what they mean and what to change.
Updated 02.09.2026
Table of contents
Faldro translates SMTP server responses into plain-language messages and always adds the server's literal response ("Server responded: …"). Below are all the messages you might see in the connection test, in the migration wizard, and when sending.
| Message | What to do |
|---|---|
| Server rejected the login or password | Check whether the username is the full e-mail address and whether the password has changed. Sending may use a different password than receiving — enter it in the "sending password" field. |
| This provider doesn't accept a regular account password | Generate an app password in the provider's panel and enter that instead of the password. |
| Provider has disabled password login for this mailbox | Microsoft 365: an admin enables "Authenticated SMTP" for this mailbox in the admin centre. |
| Couldn't establish an encrypted connection | The encryption doesn't match the port: 465 = SSL/TLS, 587 = STARTTLS. Change one of the two. |
| Port doesn't match the chosen encryption | Same as above. Port 25 also uses STARTTLS, but is blocked for clients by most providers. |
| Couldn't resolve the server name | A typo in the hostname. Copy it from the provider's panel. |
| Server refused the connection on this port | Wrong port, or your network (corporate, hotel) is blocking mail traffic. Try 587 instead of 465. |
| Server didn't respond in time | A temporary provider issue or network block. Try again shortly. |
| Server accepted the login but wouldn't send from this address | The sender address must be linked to the account you're logging in with. With some providers, add it as an alias first; with dhosting/dpoczta the domain must have mail activated (error 554 Relay access denied). |
| Provider refused the connection due to a limit | The provider's daily limit has been used up. Wait, and also check your own limit in Settings → Domains and deliverability. |
| Mailbox exists but is blocked or inactive | Contact the provider or the domain admin. |
The message "went out" but wasn't delivered
That's a different problem: the server accepted the message, but the recipient doesn't have it. Check the delivery log — it shows what the recipient's server replied.
Bounces
Messages bounced back by the recipient's server land in the Bounces folder with a summary of the reason. The most common: a non-existent address, a full recipient mailbox, rejection by an anti-spam filter (in that case see domain readiness).
Contact the team
Write to hello@faldro.com. Include your organisation address and, if possible, the subject or Message-Id of the message you are asking about.