Is it permissible to use the expression “greetings” or “best wishes”?
Question

                At the end of official communications between government departments it says “with my compliments (la lakum tahiyyaati)” or “with our compliments (wa lakum tahiyyaatuna).” But it is well known that al-tahiyyaat (greetings or compliments) are only for Allaah alone, with no partner or associate. [As said in the tashahhud in prayer].  What is your opinion on that?.
Praise be to Allah.
      There is nothing wrong with one person saying to another, 
      “with my compliments (la lakum tahiyyaati)” or “with our 
      compliments (wa lakum tahiyyaatuna)” and other such phrases. 

    With regard to the tahiyyaat that are for Allaah alone, that 
    refers to perfect tahiyyaat, as in the tashahhud in prayer: “Al-tahiyyaatu 
    Lillaahi wa’l-salawaat wa’l-tayyibaat (all compliments, prayers and pure 
    words are for Allaah).” 

    But there is nothing wrong with the greetings or compliments 
    that are given by one person to another. 

    Shaykh Muhammad ibn Saalih al-‘Uthaymeen (may Allaah have 
    mercy on him) was asked about these words, “arjuka (I hope that 
    you…)”, “tahiyyaati (my compliments)”, “an’am sabaahan (good 
    morning)” and “an’am masaa’an (good evening)”. 

    He replied: 
There is nothing wrong 
    with saying to someone, “I hope that you…” with regard to something that he 
    can fulfil your hope in. The same applies to saying, “My compliments to you” 
    and so on, because Allaah says (interpretation of the meaning): 

    “When you are greeted 
    with a greeting, greet in return with what is better than it, or (at least) 
    return it equally”

    [al-Nisa’ 4:86]
Similarly there is 
    nothing wrong with saying “Good morning” or “Good evening” etc, so long as 
    these are not adopted as greetings instead of the salaam that is prescribed 
    in sharee’ah. 

    Al-Manaahi al-Lafziyyah 
    (question 8). 

    In questions 9 and 20, the Shaykh was also asked about the 
    phrases “with our best wishes (wa lakum tahiyyaatuna)” and “I give 
    you my compliments (uhdi lakum tahiyyaati).” 

    He replied: 

    There is nothing wrong with the phrases “with our best wishes 
    (wa lakum tahiyyaatuna)” and “I give you my compliments (uhdi 
    lakum tahiyyaati)” and other similar phrases. Allaah says 
    (interpretation of the meaning): 

    “When you are greeted 
    with a greeting, greet in return with what is better than it, or (at least) 
    return it equally”

    [al-Nisa’ 4:86]
It is 
    permissible for one person to give greetings or compliments (tahiyyaat) to 
    another, but tahiyyaat in the general sense belongs to Allaah, as we also 
    say “Praise be to Allaah”, and “Thanks be to Allaah,” but at the same time 
    it is also valid to say, “I praise So and so for doing such and such” and “I 
    thanked him such and such”. Allaah says (interpretation of the meaning): 

    “give thanks to Me and to your parents”

    [Luqmaan 31:14]
And Allaah knows best.