Can I return a christmas greeting back to my christian friend ?

Salam

I have a christian friend who always sends me greetings on eid ,is it ok to send a christmas greeting back ?If not ,how am I supposed to return hospitality ?
just to add ,this is my sons former teacher ,we are only friends through mail

wa `alaykum assalaam

1) It is not permissible to take the non-Muslims as friends

http://islamfundamentals.wordpress.com/2009/05/15/taking-non-muslims-as-friends/

2) Ibn al-Qayyim, may Allaah have mercy on him, said in Ahkaam Ahl al-Dhimmah: “Congratulating the kuffaar on the rituals that belong only to them is haraam by consensus, as is congratulating them on their festivals and fasts by saying ‘A happy festival to you’ or ‘May you enjoy your festival,’ and so on. If the one who says this has been saved from kufr, it is still forbidden. It is like congratulating someone for prostrating to the cross, or even worse than that. It is as great a sin as congratulating someone for drinking wine, or murdering someone, or having illicit sexual relations, and so on. Many of those who have no respect for their religion fall into this error; they do not realize the offensiveness of their actions. Whoever congratulates a person for his disobedience or bid’ah or kufr exposes himself to the wrath and anger of Allaah.”

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Brothers and sisters, I advise you to ignore the constant posts of ignorance by this indiviual ‘Arius’; of whom continues to type fallacies of which only the ignorant would be fooled

May Allaah grant those who slander the Muslims, and particularly their Scholars, a severe and painful torment. For a person to spread lies about the Scholars of this Religion is demonstrative of hate for the Sunnah and its people, and a love for their own lowly and despicable desires

How sickening it is that those who prefer their desires to the truth try to attack the Scholars by claiming ‘they had no teachers’ (truly sickening). As regards this allegation against Shaykh Al-Albaani, then his teachers including his father Al-Hajj Nooh, and Sa’eed al-Burhaanee. May Allaah have mercy on the Scholars of this Religion, and guide or rid the Muslims of their enemies