How to fix Thunderbird SMTP error 5.7.1 (access denied)
This is an outgoing (SMTP) error: the server rejected your sign-in or refused the address you are sending from. It is almost always the username, password or From address in your outgoing server settings. Jump to your situation below or work through the methods in order.
By Neeraj Singh ~6 min Updated Jun 2026 90% found this helpful
Error message
5.7.1 Access denied / Sender address rejected. The outgoing server refused the message.
Summary
Error 5.7.1 in Thunderbird comes from the outgoing (SMTP) server and means it refused to accept your message, either because it rejected your sign-in or because you tried to send from an address the account is not allowed to use. By far the most common cause is that the SMTP username is not your full email address, or the saved password is wrong or out of date. It also appears when the From address does not match the authenticated mailbox, or the wrong authentication method is set. The fix lives in Account Settings, Outgoing Server (SMTP): set the username to your complete email address, correct the password (using an app password where the provider requires one), make sure the From address matches the signed-in account, and select the right authentication method. Once the outgoing server accepts your identity, the message sends.
What this error means
Thunderbird uses two servers: an incoming one (IMAP or POP) to receive, and an outgoing one (SMTP) to send. A 5.7.1 reply comes from the SMTP side during sending, so the problem is in your outgoing configuration or what you are trying to send, not in receiving mail.
The 5.7.1 code specifically means the server denied the action. In practice that is your credentials being wrong, usually a username that is not the full email address, or the server refusing to let you send from an address you have not authenticated as. Correcting the outgoing username, password and From address clears it.
Common causes
The SMTP username is not the full email address.
The saved password is wrong or out of date.
The From address does not match the authenticated account.
The wrong authentication method is selected.
The account is not allowed to send as that alias.
The provider now requires an app password.
Expert insight
“5.7.1 is the sending server slamming the door, and nine times out of ten it is the username. People put just the part before the at-sign, but almost every provider wants the full email address as the SMTP username. After that it is the password, which on Gmail and the like now has to be an app password, not your normal one. Get the outgoing username and password right, make sure you are sending from the address you actually logged in as, and it goes straight through.”
Manager, Tech Support & Operations · 19+ years fixing Windows and system errors
✓ How to fix it
Method 1
Set the SMTP username to your full email
1Open Account Settings, then Outgoing Server (SMTP), select your server and click Edit.
2Set the User Name to your complete email address, for example name@example.com, not just name.
3Save and try sending.
Method 2
Correct the password
1When prompted, re-enter the correct password for the account.
2If the provider requires it (Gmail, Yahoo, Outlook.com with 2FA), use an app password rather than your normal one.
3Remove any stale saved password first if needed.
Method 3
Match the From address to the account
1Make sure the identity you are sending from uses the same address you authenticate with on the SMTP server.
2Sending as an alias the server has not authorised triggers 5.7.1.
3Set the From to the authenticated mailbox.
Method 4
Set the right authentication method
1In the SMTP server settings, set Authentication method to Normal password, or to OAuth2 for Gmail and Yahoo.
2Set Connection security to match the port (STARTTLS on 587, or SSL/TLS on 465).
3Save and retry.
Method 5
Send a test
1Send a test message to yourself to confirm the outgoing server now accepts it.
2If it still fails, double-check the username is the full address and the password is current.
5.7.1 is an outgoing-server problem, so make all changes under Outgoing Server (SMTP), not the incoming account. The fix is nearly always the username (use the full email address) and the password (an app password where the provider requires one). Make sure you send from the same address you authenticate with, since sending as an unauthorised alias also triggers it.
Frequently asked questions
What does Thunderbird error 5.7.1 mean?
It is an outgoing (SMTP) error meaning the server denied your message, usually because your sign-in was rejected or you tried to send from an address the account is not authorised to use.
How do I fix 5.7.1 in Thunderbird?
In Account Settings, Outgoing Server (SMTP), set the username to your full email address, correct the password, match the From address to the account, and set the right authentication method.
Why is my username wrong?
Most providers require the full email address as the SMTP username, not just the part before the at-sign. Using only the first part is a common cause of 5.7.1.
Do I need an app password?
For Gmail, Yahoo and Outlook.com accounts with two-factor authentication, yes. Use an app password or OAuth2 instead of your normal password for the outgoing server.
Why does the From address matter?
The SMTP server only lets you send from the address you authenticated as. Sending from an alias it has not authorised causes a 5.7.1 sender-rejected error.
Is this a problem receiving mail?
No. 5.7.1 is an outgoing (SMTP) error that only affects sending. Receiving uses the incoming IMAP or POP server, which is configured separately.
Still not working?
If the username, password and From address are all correct but 5.7.1 continues, the provider may block the sign-in as suspicious from a new app. Check the account's security or recent-activity page in webmail and approve Thunderbird, then enable an app password or OAuth2. You can also submit your error to us for a tailored fix.
