Different providers have different spamfilters, different rules regarding html mails, attachment file size, use of tls, policies regarding exspired certificates, and might have different log in procedures, so yes, if there are problems the question which providers are involved.
When people say they are sending emails, do you also ask them which email provider they use to correct them?
Different providers have different spamfilters, different rules regarding html mails, attachment file size, use of tls, policies regarding exspired certificates, and might have different log in procedures, so yes, if there are problems the question which providers are involved.