Error Message when sending

[BobH7500]

When sending email from an Office 365 Exchange server account in Incredimail, I get the following error message. 550.5.6.11
"Your message contains invalid characters (bare line feed characters) which the email servers at (nyc.rr.com) don't support)

email address - ellie@ekgtalentgroup.com
Incredimail 2.5
Windows 10
outgoing mail server - smtp.office365.com
(check box checked) my servers requires authentication

Advanced settings
Outgoing port 25 This server requires a secure connection (SSL) (there are no other options in incredimail for other secure connections like TSL
I hope this information helps.
Thanks for your help in this matter
Bob Hennessy