'Had' in this usage goes with the past participle of the verb, in this case, 'to send' the past participle of which is 'sent', so 'I had sent a mail to Ryan' is correct, it is past perfect. However if you are going to use past perfect in this case you need to follow it with something, 'I had sent a mail to Ryan before I received yours.' for example.
Otherwise use the simple past, 'I sent a mail to Ryan.'
Bhaisahab, can you please tell me the contraction in sentence. Because when I read a novel or a magazine I can see a lot of contractions in most of the sentences. Sometimes I can understand its meaning. sometimes I cannot understand the meaning. Is there any solution for knowing that part.