GoDaddy recently updated their mail servers to outlook.office 365. Now I can not send emails to only certain addresses such as att.net & yahoo.com. Emails are returned with error message. I have my settings to port 587 and security to STARTTLS. It appears Thunderbird is using something that these emails won't accept. I don't want to change from Thunderbird. I've tested with other servers and there are no problems. What is the issue here? Error message: Your message to denali8@att.net couldn't be delivered. Your message contains invalid characters (bare line feed characters) which the email servers at att.net don't support. llamas Office 365 denali8 Action Required Recipient Bare line feeds unsupported How to Fix It It appears that your email program added invalid characters (bare line feed characters) into your message when you sent it. Try using a different email program to send your message. If the problem continues send this non-delivery report (NDR) message to your email admin for assistance. Was this helpful? Send feedback to Microsoft. 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. Original Message Details Created Date: 8/13/2022 3:05:10 PM Sender Address: llamas@shagbarkridge.com Recipient Address: person@att.net Subject: BOD Error Details Reported error: 550 5.6.11 SMTPSEND.BareLinefeedsAreIllegal; message contains bare linefeeds, which cannot be sent via DATA and receiving system does not support BDAT DSN generated by: DM6PR16MB2955.namprd16.prod.outlo