Does Qur'an 4:86 ("greet in return") apply to women when greeted by a non-mahram man?

Question

We're supposed to return the salam; see Islam Q&A and

And when you are greeted with a greeting, greet [in return] with one better than it or [at least] return it [in a like manner]. Indeed, Allah is ever, over all things, an Accountant.
_{Qur'an 4:86}

Sometimes non-mahram men say salam to me (e.g., through instant messaging). If I respond to the salam, then I enter into a conversation, and sometimes they talk about incrementally less appropriate topics, to the point where (after a while) I'm unsure if I've done something haram.

I'm wondering if it's best, in these circumstances, to simply not return the salam (particularly when the non-mahram man has previously engaged in inappropriate conversation).

Question: Does Qur'an 4:86 ("greet in return") apply to women when greeted by a non-mahram man?

Answer 1

Greeting non-mahrams is considered makruh and it is not required to return such a greeting:

ويكره أن يسلم على امرأة أجنبية (غير زوجة له ولا محرم) إلا أن تكون عجوزاً أي غير حسناء، أو ألا تشتهى لأمن الفتنة

...

ومن سلم في حالة لا يستحب فيها السلام مما سبق، لم يستحق جواباً لسلامه

And it is makruh to say salam to a woman who is a stranger (not a wife or a mahram) except one who is old and not attractive and there is no risk of temptation or sin.

...

When someone says salam in one of the mentioned states in which it is not desirable, then they do not deserve a reply.

^{— الفقه الإسلامي وأدلته}

وأما التسليم على النساء فجائز إلا على الشابات منهن خوف الفتنة من مكالمتهن بنزعة شيطان أو خائنة عين . وأما المتجالات والعجز فحسن للأمن فيما ذكرناه ؛ هذا قول عطاء وقتادة ، وإليه ذهب مالك وطائفة من العلماء

ومنعه الكوفيون إذا لم يكن منهن ذوات محرم وقالوا : لما سقط عن النساء الأذان والإقامة والجهر بالقراءة في الصلاة سقط عنهن رد السلام فلا يسلم عليهن

Greeting women with salam is permitted, except for young women with whom there is fear of fitnah from the whisper of satan or the treachery of the eye. As for old women, it is good to greet them as there is security as we have mentioned. This is the saying of 'Ata and Qatada, and this is the madhab of Malik and a group of the ulema.

And those of Kufa forbid it, unless they are mahrams. They say: When women are exempt from adhan, iqamah and loud recitation in prayer, then they are also exempt from replying to salam, nor will the greeting be initated with them.

^{— Tafsir al-Qurtubi}

Answer 2

Responding to greeting is wajib. Not engaging isn't wajib. Doing better is only recommended, not doing better isn't haram.

Respond to his greeting but then feel free to do as you please. Apply your God-given wisdom and common sense to do as you please. If you feel like it you can just walk away.