How to Increase the Outlook Attachment Size Limit
When sending an email attachment in Outlook, you may receive an error message warning you that the attachment size exceeds the allowable limit. When your mail server allows messages up to 25 MB and your attachment is slightly over the default 20 MB limit, change Outlook’s default to match the mail server’s default size.
Outlook File Size Limit
By default, Outlook does not send email messages with attachments that exceed 20 MB, but many mail servers allow 25 MB or larger attachments. If your email server allows larger attachments, instruct Outlook to send messages larger than 20 MB. You can also avoid getting undeliverable messages if Outlook’s default is larger than what you can send through your mail server.
Outlook 2019 and 2016: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\\PreferencesOutlook 2013: HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\\PreferencesOutlook 2010: HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\\Preferences
The default value (when MaximumAttachmentSize is not present) is 20 MB or 20480.For no attachment file size limit, enter 0. Most mail servers have a size limit, so 0 is not recommended; you may get large messages back as undeliverable.The limit corresponds to your mail server’s limit. Reduce the Outlook limit by 500 KB to allow wiggle room.
