I have updated the program to version 4.91.

Meanwhile the rest of the operation is not showing any problem, one specific folder, and one specific sender there, is hanging up the Pegasus when I try to open one of the email.
This is happening with all the email of this sender, even the old ones we have no problem to open when we had the 4.81 program.

I did various experiments and found the problem is in the IERender and the particular way these emails are formated. They only have an attach inside, with no text but have an empty HTML section

<<<some stuff>>>
X-Return-Path: proveedores@rumbosur.com.ar
X-MDaemon-Deliver-To: angelb@rumbosur.com.ar
X-PMFLAGS: 570966016 0 1 P731LBG0.CNM

--=-M5R6wPoBFUihdzrEAnJKUw==
Content-Type: text/html; charset=utf-8

--=-M5R6wPoBFUihdzrEAnJKUw==
Content-Type: file/pdf; name=EFA001200020823_20251006093811.pdf
Content-Disposition: attachment; filename=EFA001200020823_20251006093811.pdf
Content-Transfer-Encoding: base64
<<<some stuff>>>

The empy HTML section is the one that produce the problem. If I simple edit the file and delete it, the email is opened with no problem

I simply solved the problem changing the render configuration to the BearHTML render, which seems not have problem with it.

I hope this helps someone

Angel

Thanks for reporting, this issue has already been reported and fixed for the next IER update.