Local post offices do not have postage stamps of small denomination and this has been the case for some weeks now. So people who wish to book post their wedding invitations or send small notes in open covers are in a bind.
But now post offices are using the franking machines for this purpose. However you will need to pay a small fee for each franked item.
Staff at Mylapore Head Post Office are offering this service and saving people who land up with bundles of mail the trouble of spending more if they use private couriers. Those who head to the postage counters are told to go to the franking counter here.
This being the wedding season, the demand for small postage is severe.
Franking is much cheaper than stamps when sending out bulk mail – great for things like wedding invites, as you mentioned.