The real words
The frame, word for word
Estimado senor / Estimada senoraDear Sir / Dear Madam, when you know the gender.
Estimados senoresDear Sirs, when you do not know who will read it.
Le escribo para solicitar...I am writing to apply for...
Quedo a su disposicionI remain at your disposal.
Le saluda atentamenteYours faithfully. Then your name underneath.