I have three issues: No custom tld domain for premium? I like the service but want use my own domain, because some signups forbid subdomain emails. Spam or to

I have three issues: No custom tld domain for premium? I like the service but want use my own domain, because some signups forbid subdomain emails. Spam or too big attachments won't deliver. There is no spam folder? so I will never get the email even it's no spam. The attachment size is way too small if I get an invoice pdf eg. That means that service can only used for unimportant websites.