This bugfix adresses several bugs in MailHost. Some of these bugs are fixed in Zope 2.4.0 and later and some of the are valid for all versions of Zope.
The 1.4 version is a "monkeypatch" made for Zope 2.3. It might work with Zope 2.4-2.5.1, but that is not tested.
The 2.5.1 version is made for Zope 2.5.1, but will most likely work with Zope 2.4.0 and later. It is not a monkey patch but is a complete replacement.
Install the fix by unzipping the file in lib/python/Products. Do not install both fixes on the same Zope instance as this at best is redundant, but most likely will break MailHost completely.
These fixes will be included in Zope 2.6 and later.