Can I increase Outlook’s attachment limit?

QIn Issue 505’s Problems Solved pages you explained to Sudhir Khanolkar why he couldn’t send a particular attachment. As part of this you mentioned that Outlook 2016 has a default attachment-size limit of 20MB, but you didn’t mention if or how this could be increased? Is it possible? My ISP also allows attachments of up to 25MB, so it seems silly that Outlook limits what I can send to 20MB. Admittedly, I can’t imagine I’d want to send bigger files very often but it’d be nice to have the option. So, is it possible?

AYou can do this but it requires a registry hack. First, though, it’s worth understanding why Microsoft chose 20MB as the default limit for attachments — and counter-intuitively that’s precisely because many ISPS restrict overall message size to 25MB.

Note that we said ‘overall message size’, and not attachment size. That’s because any email message has a certain amount of ‘digital overhead’ that must be factored in, on top of any attachment. Typically this will be only a few kilobytes, but if an email conversation goes back and forth a few times, then the thread’s text content can quickly grow in size. If a participant then decides to add, say, a 24MB attachment, the message size could easily go beyond the 25MB overall message size allowed by many ISPS.

In this context Outlook’s default limit does make sense. If you still want to change it then, as we said, you’ll need to make a change to the Windows registry — so be sure to back up your PC first. Then, press Windows key+r, type regedit and press Enter. Use the left-hand pane to navigate to HKEY_CURRENT_ User\software\microsoft\ Office\16.0\outlook\ Preferences.

For the benefit of other readers, older Office/ Outlook editions will be have an edition number other than 16.0, so navigate accordingly (it’s 15.0 for Outlook 2013, for example).

Now, in the right-hand pane, look for a value called Maximumattachmentsize. If it’s not there, right-click in the righthand pane, choose New followed by ‘DWORD (32-bit) Value’, then type Maximumattachmentsize as the ‘Value name’ and click OK. Finally, right-click the Maximumattachmentsize value, and type a figure into the ‘Value data’ field. Typing 0 will enable any size, or type a specific figure in megabytes (MB) — 25600 for 25MB, for example (see screenshot).