why don't You ask Your other question here at the forum:
is the componentn available for jooml 4 event in a beta stage ?
I don't know which Joomla 4 event You mean, but my information for Joomla 4 is, that the core team developers promise, all extensions, which work with Joomla 3.9 also will work with Joomla 4. The current version of BwPostman works with Joomla 3.9, so there is no need for a beta for Joomla 4.
By the way, the mail address You entered at the contact form does not work:
550-5.1.1 The email account that you tried to reach does not exist.
Problem gelöst? Dann bitte auf gelöst klicken. Über ein Danke freue ich mich immer.
Problem solved? Please click to solved.I am glad to every thank you.