Troubleshooting Email Delivery Errors (SMTP)

Modified on Tue, 10 Mar at 11:41 AM

When you send a document (Invoice, Purchase Order, etc.) via email from Erplain after enabling SMTP, the system uses your own Email provider's server. If a delivery fails, Erplain will display an error message directly from that server.

This guide helps you identify if the issue is a setting in Erplain or if you need to contact your email service provider.

Reading the Error

Most email errors follow this pattern: Expected response code "250" but got code "XXX" with message "..."

250 is the expected code, the sign that everything has gone well.
Any other code (535, 550, 421, etc.) is a rejection message from your email provider, not Erplain.

There are 4 categories of codes, each starting with a different number:

2xx (success)
3xx (redirection)
4xx (temporary failure)
5xx (permanent failure)

Identifying the Source

1/ Errors from the email Provider (External)

These errors mean Erplain is working correctly, but your email server rejected the request for another reason.

Error Code	Meaning	Explanation
535	Authentication Failed	Your password or username is incorrect. If you have two-factor authentification enabled, you likely need an "App Password."
550 5.7.60	Permission Denied	You are trying to send as a different email than the one you logged in with. Check your "Send As" permissions.
554 / 550	Spam / Blocked	Your Email provider flagged the email as spam or the recipient's server blocked your IP address.
421 / 451	Temporary Failure	Your server is busy or down. Wait 15 minutes and try again.

Who to contact: Your internal IT department or your email provider (Microsoft 365, Google, etc.).

2/ Errors from Erplain Settings (Internal)

These errors usually happen during the initial setup or if settings were changed.

Error	Meaning	Necessary action
Connection Timeout	Hostname/Port issue	Check that your SMTP Host (e.g., `smtp.office365.com`) and Port (usually `587`) are correct.
Certificate Error	Encryption mismatch	Ensure your "Encryption" setting (SSL or TLS) matches what your provider requires.
Missing From Field	Configuration error	Ensure your "Reply-to" or "From" email is filled out in Erplain's SMTP settings.

Who to contact: Erplain Support.

Relevant points of contact

Error message	Point of contact
"Invalid Credentials" or "Authentication failed"	Your IT / Email Provider
"Client does not have permissions to send as this sender"	Your IT / Email Provider
"Connection could not be established" (Timeout)	Erplain Support
"Message rejected" or "Spam detected"	Your IT / Email Provider
"Relay access denied"	Your IT / Email Provider

TIP

Using Microsoft 365? Most "550" and "535" errors are solved by creating an App Password or ensuring SMTP AUTH is enabled in your Microsoft Admin Center.