There could be also a problem with f25 branch which hasn't been created at all.

I was able to create f25 branch using pkgdb web interface, but fedpkg build still fails with:

FAILED: BuildError: package sstp-client is blocked for tag f25-updates-candidate

Reviewing the logs:

{{{
$ git log
commit 35a9c870ac0ce9d1c01e93929dea2513d9bfb366
Author: Marcin Zajaczkowski szpak@users.sourceforge.net
Date: Fri Jul 22 00:18:51 2016 +0200

Fix rpmlint remarks

commit f6ef199fd034058ec26b62265af8840a0a5a3574
Author: Marcin Zajaczkowski szpak@users.sourceforge.net
Date: Thu Jul 21 23:00:14 2016 +0200

Revert "2016-05-19: Retired orphaned package, because it was orphaned for"

This reverts commit e2f384689d39f5758b3127a927b9dbb2967bb5c3.

commit e2f384689d39f5758b3127a927b9dbb2967bb5c3
Author: Till Maas opensource@till.name
Date: Thu May 19 22:44:39 2016 +0200

2016-05-19: Retired orphaned package, because it was orphaned for
more than six weeks.

}}}

So the package was not just orphaned, it was retired, and it was retired for a period of more than two weeks (see the date ranges in the above log).

Please see the wiki for orphaned packages:
[https://fedoraproject.org/wiki/Orphaned_package_that_need_new_maintainers]

In particular:

{{{
Retiring packages
Orphan packages will be retired if they remain orphaned for six weeks.
}}}

and

{{{
Un-Retiring long-time retired packages
Packages that are retired for Rawhide for more than two weeks need to be reviewed again before they can be un-retired. This is also true for EPEL-only packages.
}}}

So you are required to complete the new package review process.

[https://fedoraproject.org/wiki/Package_Review_Process]

Best Regards

So you are required to complete the new package review process.

I know. Without that I would not be able to unretire the package. The approved review request is here:
https://bugzilla.redhat.com/show_bug.cgi?id=1358956

I have already SCM access to that package. Is there anything else I need to do to make those branches unblocked?

There seems to have been a misunderstanding. The package is now unblocked. Thank you for your understanding.

Thanks @till. Everything work fine now.