Using Classic Outlook on Windows for personal email, calendar, and contact management
Hi, Peaches Llanto
Thanks for posting into our community.
According to your description, the issue of your concern that you cannot receive emails from third-party Sendgrid.
Please be kindly to understand that this would relates to Sendgrid's sever which is different from Exchange online of Microsoft.
Therefore, please contact the support from their-side for further help.
Thanks for your time and your understanding would be highly appreciated.
Sincerely,
Zed | Microsoft Community Moderator.