While ProtonMail is widely recognized for its security and privacy features, there may be instances where it's not accepted due to various reasons: Compatibility: Some platforms or services may not be compatible with ProtonMail or have not integrated it into their accepted email providers. Perception: Occasionally, individuals misread the robust privacy features of ProtonMail as a means for conducting unauthorized activities, which results in their refusal to accept it. Regulations: In some regions or within certain organizations, there may be regulations or policies that prevent the use of ProtonMail.