Email Errors

If experiencing errors when trying to Send Email, the information below may be helpful.

The most common reason for email errors is incorrect information entered in Email Setup. If sending email fails, follow these general steps:

Email Settings by Host

We have gathered settings for some email hosts. These settings may change at any time so always rely on the settings provided by the email provider.

Username Use SSL? Outgoing SMTP Server Outgoing Port Incoming POP3 Server Incoming Port
Alaska Communications checked 587 or 465 995
AOL checked 587
Aspida checked 0 0
AT & T checked 465 995
Brinkster unchecked 25
Comcast checked 587 or 465
Cox Communications checked 465 995
Einstein Medical checked 587 995
EnGuard checked or 587 or 465
FatCow (Roundcube) checked 465
GoDaddy unchecked 25 or 465
Hotmail checked or 25 or 587 995
Hushmail Hushmail Email Address checked 465 or 587
iCloud (Mozilla Thunderbird) checked 587
iCore checked 465
IONOS ( checked 587
Just Host checked 465 995
Luxsci checked 587
Officite checked 587 995
MSN Live checked 587
NameCheap checked 587 or 465 587 or 465
Optimum unchecked 25 unchecked 587
Prosites (Roundcube) checked 465 or 10465 or 11465
Rackspace checked 465
Roundcube checked 587
SendInc SendInc alias email address checked 465
Sesame checked 465 995
Solution 21 unchecked 25
Time Warner (Insight) checked 587
TNT checked or 587 or 25 143
Verizon checked 465
Yahoo checked 465 995
Zoho checked 465

Specific Errors & Solutions

If you receive any of the following errors, it means the username and/or password entered in General Email Settings is invalid.

Error: Mailbox Unavailable. The server responses was: #5.1.0 Address rejected.

Solution 1: Patient's email address is invalid. Send a test email to yourself to verify the message is only when using the patient's email address.

Solution 2: If sending from a new email address, check your inbox and open another email. This may activate the email address. Send another test to check.

Error: The operation has timed out.

Solution: Do some research and find out what port your email provider recommends, then try it. For example, for Gmail with SSL, port 465 has worked for sending emails with attachments.

Error: All confirmation emails failed.

Solution: This can happen if the subject line of the email mistakenly includes the body of the message. Check Setup Recall to make sure the subject line has a reasonable amount of words.

Error: Mailbox name not allowed. The server response was: sorry, that domain isn't in my list of allowed rcpthosts.


Error: Command not implemented. The server response was :5.5.41. Unrecognized command. z28sm22907yhn.7

Solution: In Email Setup, check the SSL box. Another possibility is to verify the password is correct. Some computers connected to the network and using the same email setup in Open Dental may be able to still use the email service if this box is unchecked.

Error: The remote certificate is invalid according to the validation procedure.

Solution: In Email Setup, uncheck the SSL box.

Error: Service not available, closing transmission channel.

Solution 1: Try a different outgoing port.

Solution 2: It could be caused by antivirus software.

Error: Open Dental appears to have successfully sent email, but recipient never receives it.

Solution: Your mail server may block outgoing mail if too many emails are sent at one time. Contact your provider to change the setting.

Error: Email fails to send and an error message reads: "Transaction failed. The server response was: 5.7.1 <>: Recipient address rejected: Access denied.

Solution: SMTP server will not relay the message; this is usually due to an incorrect password.

Error: Keyset does not exist.

Solution: Run Open Dental as administrator.

Error: Mailbox unavailable. The server response was: (WS-SVR) []:12345 is currently not permitted to relay.

Solution: Contact your email domain provider and have them allow the relay from Open Dental.

Error: Error retrieving email messages: The stream used to retrieve responses from was closed.

Solution: Check your incoming email settings in Email Setup.

Error: Error retrieving email messages: The handshake failed due to an unexpected packet format.

Solution: This error can happen if your email address is not configured properly. Specifically, if your email account uses SSL and you do not have the SSL option enabled, or if you have SSL enabled and your email account does not use SSL. See Email Setup.

Problem: In the Email Inbox or Progress Notes, email preview and message is showing in HTML code.

Solution: This means the email was sent using Rich Text/HTML format instead of Plain Text.

Problem: An incoming encrypted message is not decrypted.

Solution: This happens when decryption fails. Usually decryption happens automatically when the message is received. However, if the email is from an address with a security certificate that is not trusted, your private decryption key is not installed on the local computer, or the encryption is not in the correct format, decryption fails. To see encrypted email options, see Email Encryption Options. To add a certificate to your trusted list or retry decryption. see Email Client, When Decryption Fails.

Error: Failed to send. Error message from the email client was: Failure sending mail.

Email hosts have a maximum attachment size when sending attachments from Open Dental. If the file size(s) are too large, the email will fail.

Email message cannot contain the URL [URL] as this is only allowed for eServices.

Remove the noted URL from the email message. This can occur when attempting to use an eServices short URL in an email template.

Error: Email provider is having temporary send issues. This could be due to high email demand. Please try again later.

There was an issue when attempting to send the email on the email provider's end. This is a temporary issue, and you should be able to send the email at a later time.


Error: The transport failed to connect to the server

Solution: Set the SMTP server to:

Error: The message could not be sent to the SMTP server. The transport error code was 0x80040217. The server response was not available

Solution: Yahoo is blocking "less secure" 3rd-party applications. Create an App password for use with Open Dental.


Gmail accounts should be authorized using the Sign in with Google button in Email Address Edit. If any errors occur when sending, clear tokens in the Edit Email Address window and re-authorize the account. If errors continue, ensure Open Dental version 22.1.61, 22.2.41, or 22.3.10 or greater is installed and try again. It may be beneficial to clear the tokens for Open Dental within the Google account settings.

Due to increased anti-spam measures implemented by Google, accounts may experience errors when sending. There are a variety of errors a user may receive. In general, Google requires a higher level of account authentication. See the following link for troubleshooting details:


Authorize GoDaddy accounts through Office365 using the Sign in with Microsoft button in Email Address Edit. In rare scenarios, the setting above can be used instead.

Outlook / Office 365

Microsoft accounts should be authorized using the Sign in with Microsoft button in Email Address Edit.


Error: Service not available, Not able to send message:

Solution: Use Port 587.


Error: The message could not be sent to the SMTP server. The transport error code was 0x800ccc6a. The server response was 451.

Solution: Update to the most recent version of Open Dental.


Error: Failed to send email. Error message from the email client was: Failure sending mail.

Solution: AOL may be requiring an app password that can be created in AOL Account Security.