If this happens then check the Application Event Log. If you see the message below then you need to change your registr settings

MAPISendMail: Failed to submit message. Attachments to the message exceeded the size limit set by your Administrator.

Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences

If there is a Key called MaxiumAttachmentSize then delete it or enter a value of 1000+. Setting it to zero appears to cause this error. 

Helpfull link: https://support.microsoft.com/en-ca/help/2813269/attachment-size-exceeds-the-allowable-limit-error-when-you-add-a-large 

from here: https://www.lifewire.com/increase-outlook-attachment-size-limit-1173679 

Increase the Outlook Attachment Size Limit

To change the size Outlook allows as a maximum for attachments to send:

1. Press the keyboard shortcut Windows-R.
2. Type "regedit" in the Run dialog.
3. Click OK.
4. Travel down the registry tree to the entry corresponding to your Outlook version:
   • Outlook 2010: HKEY_CURRENT_USER\­Software\­Microsoft\­Office\­14.0\­Outlook\­\Preferences.
   • Outlook 2013: HKEY_CURRENT_USER\­Software\­Microsoft\­Office\­15.0\­Outlook\­\Preferences.
   • Outlook 2016: HKEY_CURRENT_USER\­Software\­Microsoft\­Office\­16.0\­Outlook\­\Preferences.
5. Double-click the MaximumAttachmentSize value.
   • If you cannot see MaximumAttachmentSize:
     1. Select Edit | New | DWORD Value from the menu.
     2. Enter "MaximumAttachmentSize" (not including the quotation marks).
     3. Press Enter.
     4. Now double-click the MaximumAttachmentSize value you just created.

1. Enter the desired attachment size limit in KB under Value Data:.
   • To set a size limit of 25MB, for example, enter "25600."
   • The default value (with MaximumAttachmentSize not present) is 20MB or 20480.
   • For no attachment file size limit, enter "0." Practically all mail servers have a size limit, though, so "0" is not recommended; you would invariably get large messages back as undeliverable after an often long and fruitless uploading process.
   • Ideally, the limit corresponds to your mail server's limit. Reduce the Outlook limit by some 500KB to allow wiggle room.

1. Click OK.

QUICK FIX

http://blogs.technet.com/b/the_microsoft_access_support_team_blog/archive/2016/03/09/you-may-encounter-errors-with-your-accde-mde-files-and-or-wizards-after-installing-the-march-update-for-office-2010-kb3085515.aspx

1. Run regedit

2. Go to HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Common (repeat for muliple versions of MS Office)

3. Create a KEY called "Security" here by right clicking on the Common key and selecting New->Key and typing "Security"

4. Create a DWORD in the Security key by right clicking on Security, selecting New->DWORD and type in "DisableHyperlinkWarning"

5. Change the value of this DWORD to 1