Implemented finer-grained cancellation for SmtpClient
Implemented finer-grained cancellation for SmtpClient

sstraus/MailKit,jstedfast/MailKit,jamie-dainton/MailKit,dsbenghe/MailKit,matt2003/MailKit,rajeshwarn/MailKit,FubarDevelopment/MailKit,nachocove/MailKit,eino-makitalo/MailKit,mganss/MailKit