Why is there a lag time between receiving a submission via email and seeing it under submissions through the website?

There's a distinct lag...in minutes (like 5 today) between receiving an email notification and being able to view it under submissions.  Why?

 Hi, 

Thanks for reaching out to us. Everything works fine when I sent a submission test o myself; the email was received instantly. 

Your email Service provider might be delaying your submission emails. As I can see you are using custom email as sender. 

Can you please consult your email provider?

Let us know if you have more questions. 

Regards,