Praise be to Allah.
Messages that people usually sent on special occasions are of two types:
Those that people send on Eids and occasions on which it is Islamically prescribed to congratulate one another or that are sent with the aim of reminding people to do particular acts of worship that have to do with the time when they are sent, such as sending messages to remind people to pray qiyaam during Ramadan or to read Qur’aan during that month, or reminders to fast on some days of special virtue and the like. There is nothing wrong with this type in and of itself, but care should be taken to ensure that the message is good and does not contain anything that is contrary to sharee‘ah.
Those that are sent on innovated festivals and occasions that are not prescribed in Islam, such as messages sent with congratulations on the occasion of the Prophet’s birthday (al-Mawlid al-Nabawi) or the night of al-Isra’ wa’l-Mi‘raaj (the Prophet’s Night Journey and Ascent into heaven), or Valentines Day, or Shamm al-Naseem (a traditional spring festival), or the Gregorian New Year, and so on. This kind is not allowed, because it is congratulations for an innovated religious festival or one of the festivals of the kuffaar in which the Muslims are imitating them. Both of these are forbidden and it is not permissible to offer congratulations on these occasions or to co-operate in spreading such greetings.
Muslim (4831) narrated from Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (blessings and peace of Allah be upon him) said: “The one who calls to true guidance will have a reward like the rewards of those who follow him without that detracting from their rewards in the slightest, and the one who calls to misguidance will have a burden of sin like that of those who follow him, without that detracting from their burden of sin in the slightest.”
Al-Nawawi (may Allah have mercy on him) said:
The one who calls to true guidance will have a reward like that of those who follow him and the one who calls to misguidance will have a burden of sin like that of those who follow him, regardless of whether it is guidance or misguidance, and whether he is the one who started it or he was following someone else, whether it has to do with teaching knowledge or acts of worship or matters of etiquette or anything else. End quote.
Sharh al-Nawawi ‘ala Muslim, 16/227
And Allah knows best.