We have Exchange Server 2016 and Enterprise Vault 12.5. On client side we have Outlook 2016 & 2019 with EV Outlook Add-ins installed. While trying to open archived email, we are getting error "Cannot downoad the archived item from https://archive.domain.com/EnterpriseVault/download.asp. In the end Unknown error: 0x8004010F.
If this happens on some, but not all items, have a look at this KB:
It might be due to a huge number of recipients, or possibly a corrupted item.
The issue is seens across different version of Outlook like 2013, 2019 & 365.
On clicking the URL, the archive email opens in a browser instead of Outlook. Yes, we are able to access the archived email but in browser window.
Hm. Which EV Client version do you use?
There were issues with old(er) versions, caused by Outlook/Microsoft patches.
and possibly this one: https://www.veritas.com/content/support/en_US/article.100040149
Apart from the suggestions provided by @GertjanA & @CConsult, it will be very interesting to note what is seen in the Client Log of a couple of the Users. If the link is opening, that means there's no issue in the communication to the Virtual Directory on the EV Server and thereby to the underlying architecture on the Server side. It has to be something pertaining to the EV Outlook Add in on the client side. Hence the request for the client log. You can redact environment specific information for security purposes.
To collect the Client Trace you can look this article... How to perform a client trace for Enterprise Vault (EV) with Outlook 2010/2013