We have mission critical application and have been using Thunderbird email client. That has been failing on the email sends. MS logon does not come up. Not really your issue. But recommend a client we cna use that works. We are using MS Office 365 noreply.
We started DasyLab 2022 sending to smtp.office365 and it works fine to tmobile but only worked 1 time to vtext.com. I also tried the vzwpix. Returns error:
Your message contains invalid characters (bare line feed characters) which the email servers at vtext.com don't support.
More Info for Email Admins
Status code: 550 5.6.11
This error occurs when the email program or device used to create or send an email message adds bare line feed characters into the message. When bare line feed characters are included in a message, the SMTP protocol chunking feature is required to transmit the message between email servers. Chunking uses the SMTP protocol BDAT command, but the recipient's email server doesn't support the BDAT command.
To fix the issue, the sender should send the message using an email program or device that doesn't add bare line feed characters to messages. Most modern email programs don't add bare line feed characters.
If the sender is using a device like a fax machine, printer, or scanner, it's likely an older model that doesn't support the SMTP protocol BDAT command. To fix this error, you'll need to replace the device with a newer model that supports the BDAT command. The industry standard recommendation to support SMTP chunking was published in 1998 so most devices manufactured during the last decade support this feature.
Another option is for the email admin at the recipient's domain to upgrade their email servers to servers that support the SMTP protocol BDAT command. Most modern email servers support BDAT; however, some free and older email servers don't support it.
For more information see Fix email delivery issues for error code 5.6.11 in Office 365.