It isn't unreasonable to think that CT_Mailmod might be interpreted as spam, and the fact that not everyone using the addon has been banned for it doesn't necessarily imply gold buying or hacking. Without knowing their code it's hard to know for sure.
If there are commonly used addons that trigger the anti-cheat system, then that's a problem. Appealing requires a dev to look into it, which costs them time. Determining false positives is, depending on their code, probably pretty difficult. It might be worth looking closer at such potential edge-cases to at least be able to inform players "addons manipulating behavior x might be interpreted as cheating and should not be used".