Every mail server is unique, and so are their error responses. It's not always easy to decipher what they're trying to tell you, so we've collected a list of the most common error messages and their variations so you can figure out what to do about it. Look for the error message that most closely matches the one you received and use our recommendations to try to fix them.
Further reading:
7 Ways to Build Your Email List
Any listserv or mailing list service?
Email Problems: What Should I do?
How Did My Email Get Compromised and What Can I Do to Stop It?
How to Check and Send Emails Using Webmail
How to Solve Email Bounce Back Issues
"IP Address Has Changed!"
Every time you log into your webmail account, your computer's IP address is recorded. If your IP address changes while you're logged in, webmail won't recognize your new connection as valid and will automatically log you out. The easiest way to fix this error is to log in again so your new IP address is recorded. But if you're seeing this error frequently, here are a few other things you can do:
- If possible, try using another internet connection, such as a mobile data or a WiFi, and try again.
- If this resolves the issue, contact your internet service provider and ask to be given a static (unchanging) IP address so it won't change while you're logged in to webmail.
- If that isn't possible, ask if the "DHCP lease time" can be increased, which will allow your login sessions to be longer.
- Is the problem only with your webmail client? Try using a desktop email application, such as Outlook, Thunderbird, or Apple Mail. Email applications don't use your IP address as part of the authentication process, so a changing IP address isn't a problem.
Further reading:
How to grow your mailing list ethically
Managing the Mail Function in CPanel
How to create an email forwarder in cPanel
How to enable spam assasin in cPanel
How to fix error 500 no such user here
"Authentication Failed"
An "Authentication Failed" error means the email server cannot verify that your email access is authorized. This is typically due to a mistyped password, but it can also be caused by incorrect username, connecting to the wrong server, or blacklisting. Follow these steps to resolve the issue:
- Reset your email password.
- Open your email application and check the following settings:
- Update the password to your new case-sensitive password.
- Confirm your username is the full email address, such as john@example.com.
- Confirm the server name is mail.example.com where example.com is your domain name.
- Does your email application work now? If not, here are a few tips:
- If you've recently changed where your domain points, or if you've upgraded or downgraded your hosting plan, wait up to 72 hours for your new DNS settings to propagate worldwide.
- It's also possible that your local IP is blacklisted. Wait 24 hours and try again, using webmail in the meantime. If it still doesn't work after 24 hours, check out local IP could be blacklisted.
- The local IP address your email application is using may be blacklisted, which can happen after a few too many failed login attempts within a short period. If you suspect this is the problem, try using another internet connection, such as a mobile data or a WiFi, and try again. Check out If Your Local IP Is Blacklisted for more information.
Certificate Name Mismatch
This error is a warning from your email application that the certificate for SSL that the server uses doesn't match the name that your email application was expecting. Variations of this error include:
- Invalid Certificate
- Mail can't verify the certificate for example.com
- The identity of mail.example.com cannot be verified.
- The certificate for this server is invalid.
- Host name mismatch
- A secure connection cannot be established with the server.
- The name on the security certificate is invalid or does not match the name of the site.
- The server you are connected to is using a security certificate that cannot be verified.
- This Connection is Untrusted. Confirm security exception.
If your email application is set up using Private (with SSL) settings, and you're using your domain name as the mail server (such as mail.example.com), your email application expects the SSL certificate to contain your domain name, when it contains the name of the Todhost server (such as mail.todhost.com) instead. Because of this mismatch, your email application will warn you that the name on the Todhost server's certificate doesn't match your domain name. This is normal.
Email applications will allow you to continue to send and receive mail, but you may need to adjust a setting in your email application to confirm you're aware of this configuration. Each email application has slightly different steps for setup. If you aren't sure which setting to change, check out our Email Application Setup Guides.
Further reading:
7 Ways to Build Your Email List
Any listserv or mailing list service?
Email Problems: What Should I do?
How Did My Email Get Compromised and What Can I Do to Stop It?
How to Check and Send Emails Using Webmail
How to Solve Email Bounce Back Issues
"550 Sender Verify Failed"
This usually means the inbox you're sending to or from is full, or your mail routing setting in the zone editor is wrong.
- Full mailbox. Mailbox storage quotas are set to 250MB by default, but some plans allow you to turn off the limit and set mailbox quotas to "unlimited." If an email account is at or past its capacity, sending out from it won't work and you'll get a "Sender Verify Failed" error. To check on the mailbox quota of an email account follow these steps:
- Log in to your Todhost web hosting control panel.
- Go to the Hosting menu and click Email in the submenu.
- Locate the email address having problems in the list, and click view details button on the right to view detailed information about the email account.
- Look for the mailbox quota. If the account is at or exceeding its quota, increase its limit or delete emails to save space.
- Mail Routing. Your domain's email routing setting may be incorrect. Check out How to Modify MX Records: Email Routing for more information.
Bounce — but no email address returned
The recipient mail server bounced your email, but did not indicate which address it was bouncing on behalf of. You can determine the recipient based on the content of the bounce.
Challenge response
In this case, the recipient has installed software as an anti-spam measure, that only accepts email from previously authorised senders. If the software doesn't know the sender, a challenge email is returned, requiring a specific action before the original email will be sent to the user.
Since the requested response could be anything, these bounces should be treated as a soft bounce.
DNS failure
The recipient's email server is currently unable to deliver your email due to DNS issues on their end. This may or may not be a temporary problem. The error could be due to the mail server being down, or there was a typo when it was set up, or maybe the destination domain doesn't exist.
All we know is that the DNS host is unreachable, therefore you have to treat this as a soft bounce to allow some time for the problem to be rectified.
Further reading:
How to grow your mailing list ethically
Managing the Mail Function in CPanel
How to create an email forwarder in cPanel
How to enable spam assasin in cPanel
How to fix error 500 no such user here
General bounce
This is treated as a soft bounce because we cannot determine the exact reason for delivery failure. Typically this bounce type is associated with a technical issue such as, "Connection timed out", but we will also classify a bounce as "general" if the response from the recipient server is open to more than one interpretation. It could be a non-standard error message, or too vague to be useful.
Hard bounce
Your email is permanently undeliverable to this email address. The address is either fake, was entered incorrectly, or the user mailbox or domain is no longer active.
We remove the address from your mailing list and added it to your suppression list which prevents any further emails being sent to the address. This protects your sender reputation and ensures you do not pay to send to dead addresses.
Mailbox full
The email server cannot deliver your email because the recipient's inbox is full. Most email applications have a set amount of storage an individual user can use for email. If this quota is exceeded the server will not let any more mail through, but it will also usually alert the mailbox owner so they can do something about it.
So while it may be the case that your recipient hasn't put aside time to make some space, it could also be a sign of an abandoned mailbox. For example, someone sets up a free webmail account just for shopping-related emails, then stops signing in when they start saving for a house.
We treat these as a soft bounce in case it's temporary, but if the issue continues we'll convert it to a hard bounce for you.
Mail block — general
The recipient's email server is blocking inbound mail from our server, which may be due to a blacklisting. A mail block is recorded when the receiving server blocks an email completely; rejecting the message without any attempt to deliver it to the inbox.
The most likely reasons for this block are:
- Your reply-to address is blacklisted.
- One of our sending IPs is temporarily blocked.
- One of our sending domains is temporarily blacklisted.
- The receiving server only accepts whitelisted senders.
Mail block — known spammer
The recipient's email server has blocked your email on the basis of poor sending reputation. The most likely reasons you would see this block are:
- The email you have sent over time to the mail server has consistently resembled spam, and it has stopped delivering email from you to its users.
- One of our sending IPs is temporarily blocked.
- One of our sending domains is temporarily blacklisted.
You should only try resending to this mail server if the bounce is due to our IP or sending domain being blocked or blacklisted. Please contact us to find out.
Mail block — relay denied
Your email has bounced due to a temporary error, which could be on the sending or receiving side. "Relay" simply refers to the transmission of your email from our server to the receiving server, which has most likely been denied due to user error. This type of bounce usually occurs when the sender's message is not authenticated, but it can also be due to a misconfigured server on the recipient side.
Technically speaking this is a hard bounce, but we treat it as a soft bounce because it's often a result of user error, which can therefore be resolved.
Mail block — spam detected
The recipient's email server has blocked your email on the basis that the content resembles spam. This mail block is often triggered by something detected in your email content, but can also be your reply-to address or brand name that has a poor reputation.
We treat this as a soft bounce due to the fact that some mail servers and email providers respond with false or incorrect error codes.
Message too large
The size of your email — including all headers, text and images — is larger than the maximum size the recipient's mailbox allows. The bounce message returned doesn't include information on what the size limit is, but we advise you do not send messages bigger than 500Kb.
Transient bounce
The recipient mail server can't deliver your email, but will keep trying for a limited period of time. We treat this as a soft bounce, as when the recipient mail server retries the message could be delivered.
