I use Thunderbird 52.9.1 (32-bit) as email client on smpt.1and1.com server via imap. For the last week or so, I have been getting a number of emails to friends being kicked back due to errors. All of these kickbacks are from friends that are using [email protected]. They all come back with this message: "SMTP error from remote server for TEXT command, host: mx1.charter.net (68.114.188.69) reason: 552 5.2.0 Invalid 7bit DATA". I have contacted 1and1 and charter and they do not see any issues or are not any help. With 1and1, I was able to successfully send emails to these addresses without problem using the 1and1 webmail, but not using Thunderbird. I have restarted my computer and Thunderbird. Made no difference. I have checked that I am using the current version of Thunderbird. I guess I could delete and reinstall Thunderbird but would rather not. Help!