''<p>peter.f.hjort [[#question-1569763|said]]</p>'' <blockquote>To be really useful to me I need Thunderbird to be able to read my Outlook pst-files. Yet it can not do so. There is absolutely not process you can undertake to make Thunderbird read a PST file. It has no idea that it is even a mail file. <blockquote> For years my practice has been to move emails from the ost-file to the pst-file too limit the size of the ost-file. Both files are localized on my computer but only the emails in the ost-file are in my gmail-account. So the method helps me limit the size of my gmail-account but still gives me total access to my email-history. </blockquote> Except now you have encountered the primary reason computer professionals have made recommendations against using proprietary file formats to store archives for at least the last 30 years, probably longer., but that is how far back I remember it happening. Only the application that created them can actually use them without some sort of conversion. <blockquote> Without a similar possibility in Thunderbird it's difficult for me to leave Outlook, which I really want to. Can you help me? </blockquote> Thunderbird can import mail from the default outlook program installed on the system when it is installed. So if the outlook application sees the mail to export it to Thunderbird then Thunderbird will get it. If outlook does not offer it, then Thunderbird will not get the email. The import uses dynamic data exchange and relies on Outlook to offer the mail to be imported. So if you have some sort of archive you have to load, it may well be that the import will not see those emails at all. My understanding is it is only the "default" file that is imported, but as I have not used outlook for around 25 years, I have no real recent experience. You may want to invest in some Third party software to convert your proprietary files into open file formats that Thunderbird understands like EML and MBOX. Use a search engine to search PST to MBOX converter. My search even showed some in the Microsoft store. I understand that there are a lot of vendors offering such software as you are not alone in wanting to access your outlook files in software other than Outlook.