Yeah that restriction isn't immediately apparent when you look at the documentation that mailchannels link to on their site.[1] However, it is mentioned in the

Yeah that restriction isn't immediately apparent when you look at the documentation that mailchannels link to on their site.[1] However, it is mentioned in the openapi schema.[2] I suppose they intend that people send up to 20M with just text/plain and text/html. (Send all the base64 encoded images I guess) [1]https://api.mailchannels.net/tx/v1/documentation https://api.mailchannels.net/tx/v1/documentation [2]https://api.mailchannels.net/tx/v1/openapi.yaml https://api.mailchannels.net/tx/v1/openapi.yaml