I have a weird issue with some users sending emails to another company. The Exchange Admin from the other company sent me the message header where apparently when our users send messages to the user in the other company it adds an a dot/period in the middle of their last name of their email addresses. e.g. firstname.last.name@domain. When it should be fistnam.lastname@domain I have no idea where to start researching this issue. Because of that the emails never get to the intended recipients and get caught in their spam filter. I will really appreciate in anyone can help me with this.