It may happen that the emails you received are HTML only.
In such case IMail.Text is going to be empty, as there is no text/plain
Use IMail.Html or IMail.GetBodyAsText in such case.
IMail email = ...
string html = mail.Html;
string plain = mail.GetBodyAsText();
IMail.GetBodyAsText returns text/plain (IMail.Text) if it's available, if not, it parses IMail.Html and extracts plain text.