Scan-to-Email Not Working, Server Certificate & Connection Problems

Scan-to-email failures often look like generic printer or copier problems at first because the device still scans, still connects to the network, and may even pass its own email test. The actual break usually happens later, at the point where the SMTP service, account policy, certificate check, or mail-size limit decides whether the message can leave the device at all. That is why these failures can feel inconsistent: the scanner works, the test works, and yet the real document never arrives.

Problem: Scan-to-email worked with one Microsoft 365 account, but failed with other mailboxes

What users observed: A copier was configured with smtp.office365.com, port 587, STARTTLS, and app passwords, and the settings would connect successfully only with one specific administrative Microsoft 365 account. Other accounts, including accounts with SMTP authentication enabled and valid app passwords, failed with login or connection errors even though the SMTP fields looked correct.

What was tried: Multiple user mailboxes were tested, app passwords were regenerated, SMTP Authentication was checked, and licensing was reviewed. The problem did not follow one mistyped password. It followed which user account was being used.

How this played out: The issue was resolved only after the affected users were added to the exclude list in Entra under Conditional Access for the policy that blocked legacy sign-ins without MFA support. Once those users were excluded from that policy, scan-to-email started working for them as well.

Problem: The printer’s scan-to-email test succeeded, but real scans failed with a server error

What users observed: In one documented case, the device’s built-in scan-to-email test worked and the test message reached the recipient successfully, but actual scans from the control panel failed with a server error and no email was delivered. That made the copier look correctly configured even though real scan jobs still died after scanning.

What was tried: SMTP settings were left in place because the successful test message showed the basic mail path was working. The next step was checking what was different about the real scan messages compared with the device’s simple test email.

How this played out: The real cause was an internal Exchange spam filter that was classifying the printer’s actual scan messages as spam and rejecting them. Once the office’s static IP address was whitelisted, the scan-to-email jobs were delivered normally.

Problem: Gmail-based scan-to-email stopped working after Google changed account security

What users observed: A previously working scan-to-email setup that used Gmail stopped working after Google’s security changes removed support for less-secure app access. Users described cases where the device had worked for months and then stopped without any printer-side hardware change.

What was tried: Re-entering the normal Gmail password did not restore the feature, because the issue was no longer the password itself. The account was now refusing the older authentication path the device had been using.

How this played out: The working fix was to enable 2-Step Verification on the Google account and generate a Google App Password, then enter that app password into the scan-to-email profile instead of the normal mailbox password. After that, the device could authenticate again and send mail.

Problem: Scan-to-email failed and the device could not validate the mail server certificate

What users observed: Some devices reached the point of mail configuration and then failed with a certificate validation message stating that the server certificate was self-signed or issued by an unknown authority. In these cases, the issue was not that the SMTP hostname or port was wrong. The device refused to trust the server it was being asked to talk to.

What was tried: Users kept checking SMTP fields first because that is where scan-to-email usually breaks. But the error made it clear that the problem sat in trust validation rather than in the mailbox credentials.

How this played out: The path forward was to import the trusted CA certificate into the printer or copier so the device could validate the server certificate successfully. Until that trust chain was present, the device would not complete the scan-to-email connection.

Problem: SMTP AUTH was set up, but the sender address did not match the mailbox being used to log in

What users observed: Some scan-to-email failures happened even though the SMTP server, port, TLS, and mailbox credentials were all entered correctly. The break occurred because the device was trying to send mail from a different address than the mailbox used for SMTP authentication.

What was tried: Users often kept regenerating passwords or retesting the SMTP login because the account itself still worked in Outlook. That did not fix the send failure when the From address on the device did not match the authenticated mailbox.

How this played out: The working fix was to either make the device send mail from the same address used for authentication, grant Send As permission for the alternate sender, or move the device to a relay-based path if that matched the environment better. The issue was not a bad password. It was a mailbox-permission mismatch.

Problem: Large scans failed because the email attachment exceeded the allowed size

What users observed: Scan-to-email worked on smaller jobs but failed once the document became large enough. In copier environments, this showed up as scans stopping at the point where the device reached its configured maximum size, or mail servers rejecting larger jobs after the device tried to send them.

What was tried: Users kept resending the same job, assuming the mail path had failed randomly. That did not help because the job was simply too large for the configured limit or email system.

How this played out: The confirmed working directions were to reduce scan size by lowering resolution or color depth, or to use the device’s divide-and-send behavior so the job was split into smaller email-sized segments instead of one oversized attachment.

Problem: Microsoft 365 SMTP worked in theory, but the device still could not send mail

What users observed: Devices were pointed at smtp.office365.com but still failed to send mail, even when administrators were confident they had the right Microsoft 365 server. In those cases, the printer was often missing one of the required conditions for Microsoft 365 SMTP client submission, such as TLS support, mailbox login capability, or the ability to use the authenticated mailbox as the sender.

What was tried: The first assumption was often that any Microsoft 365 SMTP endpoint should work as long as the hostname and port were correct. That was not enough for devices that could not satisfy the authentication or TLS requirements of the chosen mail method.

How this played out: The fix depended on the exact failure mode: some devices needed proper mailbox credentials and TLS on smtp.office365.com, while others worked only after being moved to a relay-based send path because the device could not meet Microsoft 365’s SMTP AUTH requirements cleanly.