Hi As far as I know, exchange server won’t convert charset. So I think it is client or origin email problem. In fact, I don’t understand your meaning clearly. If my saying is wrong, please correct me. Your outbound email is US-ASCII. Inbound email becomes to be Russian Cyrillic. 1. Please send origin email to your test account like (gmail,yahoo account) and reply it. If it is not blocked, it is hard to say that it is your problem. You should communicate with outside company. If it is blocked again, it is your site problem. 1. It is client problem. Please send origin email by other client. 2. It is outlook problem, you can send origin email through owa and test it. 3. It is firewall problem, please turn off firewall and test it again. Terence Yu TechNet Community Support

Recently one of our users is having reply emails from various outside companies blocked by the Barracuda spam filters because the charset of the message is kio8-r; this is for Russian Cyrillic. There is nothing in Russian in the message, or even a single Cyrillic character. The original outbound email has a charset of us-ascii; when they come back they are now kio8-r. Since the problem is with multiple outside companies I am working on the assumption the problem is with the emails themselves and not the other company's email system. Is there something that can become corrupt in a message to make the charset appear to be kio8-r when it is not?TBrennan

Hi As far as I know, exchange server won’t convert charset. So I think it is client or origin email problem. In fact, I don’t understand your meaning clearly. If my saying is wrong, please correct me. Your outbound email is US-ASCII. Inbound email becomes to be Russian Cyrillic. 1. Please send origin email to your test account like (gmail,yahoo account) and reply it. If it is not blocked, it is hard to say that it is your problem. You should communicate with outside company. If it is blocked again, it is your site problem. 1. It is client problem. Please send origin email by other client. 2. It is outlook problem, you can send origin email through owa and test it. 3. It is firewall problem, please turn off firewall and test it again. Terence Yu TechNet Community Support

Hi Do you have anything to update your issue?Terence Yu TechNet Community Support