It is allowed for women to attend the general lectures given in the masjid.

Shaikh Salih al-Fawzaan hafiduhallah said:

“From that, it is permitted for her to attend the Masaajid to participate in the good in terms of the congregational prayer and attending the sittings of remembrance with modesty and holding fast to the precautions that will keep her away from fitnah and preserve her honor” [Mulakhas al-Fiqhi (1/210)].

Shaikh Muqbil rahimahullah mentioned that she can even attend the lessons in the masjid if she is menstruating:

Question: Is it allowed for a woman to attend the sittings of Knowledge and lessons in the masjid?

Answer: “There is no harm inshallah. The Hadith:

إني لا أحل المسجد لحائض ولا جنب

It is not permitted for a menstruating woman or one who is junub (sexually impure) to stay in the mosque [Reported by Abu Dawood no. 232]

is a weak Hadith. The Prophet (ﷺ) said:

إن حيضتك ليست في يدك

Your menstruation is not in your hand [Muslim no. 298]

And he (ﷺ) said:

أفعلي ما يفعل الحاج غير ألا تطوفي في البيت

You should perform all that a pilgrim would do, except circumambulation until you are pure (i.e. performed Ghusl) [Bukhari no. 1650 and Muslim no. 1211]

So there is no harm if she attends the lessons of Knowledge in the Masjid”.

[http://www.muqbel.net/fatwa.php?fatwa_id=3328]

As for an all women’s class in the masjid, then this was not something known in the time of the Salaf. In fact it is an innovation.

Shaikh al-Albani rahimahullah wrote in Saheeha (6/401):
“I say: as for what is recently spreading here in Damascus in terms of women frequenting the Masaajid in specific times to hear a lesson from one of them, from what they call the Daa’iyaah (Female caller) as they claim. That is from the newly invented affairs which were not in the time of the Prophet (ﷺ) nor the time of the Salaf. It was only instituted for the pious Scholars to teach them in a specific place as comes in the Hadith [See: Saheeha no. 2680] or in the lesson of the men with a barrier for them in the Masjid if it is possible. Otherwise, the men will overcome them and it is not possible for them to learn knowledge and ask about it.

If there are women today from those who have been given something of knowledge and sound fiqh based on the Book and Sunnah, then there is no harm if she establishes a specific sitting in her house or in one of the women’s house. That is better for them. How not when the Prophet (ﷺ) said regarding the congregational prayer in the Masjid:

بيوتهن خير لهن

Their houses are better for them (for praying) [Saheeh Sunan Abi Dawood no. 567]

If the affair is like this for the prayer which the woman must have etiquette and modesty, so how is knowledge in the house not more deserving? Especially when some of them raise their voices [in the class] and others participate with them [in doing so]. So their is an buzzing that comes from them which is ugly and dispraised. This is what we heard and witnessed unfortunately.

Then we have seen this newly invented matters has spread to some other lands like Oman for example. We ask Allah for protection from every innovation and newly invented matter“.

He also said in his annotation to the Hadith (no. 1999) in Saheeh Targheeb was-Tarheeb (2/442):

“…The routes of this Hadith have been mentioned in Saheeha (2680) and I have mentioned there that it is an innovation for a woman to teach in the masjid with women as some do in Damascus and other than it. Our Prophet (ﷺ) spoke the truth when he said:

بيوتهن خير لهن

Their houses are better for them (for praying) [Saheeh Sunan Abi Dawood no. 567]

[Taken from Qamoos al-Bid’ah (pg. 430-431)]

Note: Women who are coming to the masjid must be dressed appropriately according to Islamic regulations. If they are not dressed appropriately, they are not allowed to come to the masjid.

عَنْ عَمْرَةَ بِنْتِ عَبْدِ الرَّحْمَنِ، أَنَّهَا سَمِعَتْ عَائِشَةَ، زَوْجَ النَّبِيِّ صلى الله عليه وسلم تَقُولُ لَوْ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم رَأَى مَا أَحْدَثَ النِّسَاءُ لَمَنَعَهُنَّ الْمَسْجِدَ كَمَا مُنِعَتْ نِسَاءُ بَنِي إِسْرَائِيلَ ‏.‏ قَالَ فَقُلْتُ لِعَمْرَةَ أَنِسَاءُ بَنِي إِسْرَائِيلَ مُنِعْنَ الْمَسْجِدَ قَالَتْ نَعَمْ

Amra, daughter of Abd al-Rahmin, reported:
I heard ‘A’isha, the wife of the Messenger of Allah (ﷺ). say: If the Messenger of Allah (ﷺ) had seen what new things the women have introduced (in their way of life) he would have definitely prevented them from going to the mosque, as the women of Bani Isra’il were prevented [Muslim no. 445]

Imam Shawkaani rahimahullah said:

“It occurs from the aforementioned Ahaadith in this chapter that the permission given to the women from the men to go to the masjid is only if there is not along with their going out anything that calls to fitnah in terms of perfume, jewelry or any adornment, which is obligatory upon the men. It is not obligatory [for her to go] with the presence of what calls to fitnah nor is it allowed. It is prohibited for them to go out due to his (ﷺ) statement:

فلا تشهدن

“…let her not attend…” [Muslim no. 444]

[Nayl al-Awtaar (3/161)]

Imam Sa’adi rahimahullah said:

“…If they come out in adornment, perfume, and good form, then it is prohibited for them to come out and it is obligatory upon her guardian, the Islamic ruler, and whoever has ability to prevent her from coming to do so. This is because if she is safe from temptations herself, then she will tempt the people. So whoever sees her and is tempted or follows her with his eyes, then his sinful and she is also sinful because she is the cause. Also, the one who it is obligatory to prevent her from coming is also sinful [for not doing so] and in Allah aid is sought” [Ta’leeqaat ‘ala Umdahtul-Ahkaam pg. 94]

And Allah knows best
Faisal Ibn Abdul Qaadir Ibn Hassan
Abu Sulaymaan