With my favourite suggestion, a direct ingame mail system, still impossible after nine years, let’s try asking for something different.
A plain forum feature for guilds should be possible to integrate with reasonable effort. It does not need to go any further than pure text postings, it does not need any formatting features, troop code conversion, colours or smileys (the only luxury I suggest would be line breaks), and if you are worried about server space, you can put severe limitations on the amount of threads as well. Moderation can be directly linked to the existing guild titles.
The amount of chat messages to display is limited (as Eika’s thread, that brought me on this thought, points out again), the length of announcement messages even more.
If you integrate this, guilds have a place for texts, that are meant to stay or at least to be visible for a bit.
Especially in Tower weeks like this one, it would help a lot.