Announcing wedding invitations in the mosque
Question

In our country, wedding invitations involve inviting everyone in our village and in the neighbouring village, by going house-to-house to invite people. If someone is not invited from his house (by a personal visit), he does not regard that as an invitation. The village has expanded a great deal, as has the neighbouring village, and people are living on the outskirts and on the mountaintops, which has made it very difficult to invite each person from his house, and that has caused the people a great deal of hardship. The people have agreed to announce the wedding invitation in the mosque. Is this permissible or haraam?
Praise be to Allah.Firstly: 
The mosques should be free of announcements that have to do with worldly matters, which include telling people about a wedding feast or inviting them to it, because the mosques were not built for that; rather they were built to establish worship, teach knowledge, and spread goodness. Muslim narrated in his Saheeh (568) that Abu Hurayrah (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “Whoever hears a man making a lost property announcement in the mosque, let him say: May Allaah not restore it to you, for the mosques were not built for this purpose.” 
In Saheeh Muslim (569) it is also narrated from Sulaymaan ibn Buraydah, from his father, that a man made a lost property announcement in the mosque, saying: Who has found the red camel? The Prophet (blessings and peace of Allah be upon him) said: “May you not find it. The mosques were only built for that for which they were built.” 
But it is permissible to make announcements concerning worldly matters outside the mosque, even if that is by posting a flyer on the outside wall. 
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked: What is the ruling on putting some announcements in the mosque, such as announcing a trip for Hajj or ‘Umrah, or announcing some lectures or classes? 
He (may Allah have mercy on him) replied: If the announcement has to do with acts of worship, there is nothing wrong with that, because acts of worship are means of drawing closer to Allah, and the mosques were built for the worship of Allah, may He be glorified and exalted. 
But if it has to do with worldly matters, then it is not permissible. But they may be announced on the outside walls of the mosque. Trips for Hajj come under the heading of worldly matters, so we do not think that they should be announced inside the mosque. 
Circles of dhikr, such as lessons and classes, are purely good, so there is nothing wrong with announcing them inside the mosque, because they are good. 
End quote from Sharh Manzoomah al-Qawaa‘id al-Fiqhiyyah, p. 52 
He (may Allah have mercy on him) also said: It is not permissible to put up posters for Hajj and ‘Umrah inside the mosque, because usually these trips are organised with the aim of financial gain, so they come under the heading of trade or business. But instead of being inside the mosque, they may be put up at the door of the mosque on the outside.
End quote from Liqaa’aat al-Baab al-Maftooh, no. 151, question no. 10 
Shaykh Ibn Baaz (may Allah have mercy on him) said concerning lost property announcements: As for writing them on a piece of paper, if it is put up on the outside wall of the mosque, there is nothing wrong with it.
End quote from Fataawa ash-Shaykh Ibn Baaz, 30/9 
Based on that, you can write the wedding invitation on a piece of paper that is put up on the outside wall of the mosque, or you could distribute the invitation to the worshippers outside the mosque. 
However, we think that it is possible to overcome this difficulty by making phone calls or sending text messages and the like. With the expansion of the village that you mention, it does not seem that the one giving the invitation wants to invite all the people. Rather whoever he wants to invite and cannot contact him in person, he can contact him by phone or send him a message and the like. 
Thirdly: 
The majority of fuqaha’ are of the view that it is mustahabb or encouraged to do the marriage contract in the mosque. They quote as evidence for that the hadeeth. “Announce this marriage, do it (the marriage contract) in the mosque and beat the daffs (hand drums) for it.” Narrated by at-Tirmidhi, 1089. But this hadeeth is da‘eef (weak), as stated by al-Albaani in Da‘eef at-Tirmidhi. However he classed as hasan the phrase “Announce this marriage”, as stated in Aadaab az-Zafaaf, p. 111 
See also the answer to question no. 87898
It is not permissible to believe that doing the marriage in the mosque is Sunnah, because there is no proven evidence to that effect. However, it is something permissible, so if they do the marriage contract in the mosque then move to the place where the waleemah (wedding feast) is being given, they will have made the announcement of the wedding. 
And Allah knows best.