This article explains how to increase the maximum Outlook attachment size limit. Instructions apply to Outlook 2019, Outlook 2016, Outlook 2013, Outlook 2010, and Outlook for Microsoft 365.
When you send an email attachment in Outlook, you may receive an error message warning that the attachment exceeds the allowable size limit. If your mail server allows messages up to 25 MB and your attachment is slightly larger than the default 20 MB limit, change the Outlook default size to match the mail server's default size.
Type regedit in the Run dialog box.
Navigate through the registry tree and locate the entry that corresponds to your Outlook version:
