Exit the sane idea of a simple phone call to tell the invitee about date & time of the event. Enter the multi-layered invitation process. The parent of the bride calls this person over the phone and lets them know their daughter is getting married and that an invitation is on the way. Then the actual invitation is sent "cordially inviting" this person. But a bland invitation won't do. So a post-it note is stuck inside asking the person to consider this "as a personal invitation" and attend. 1 week after the invite is sent , a confirmation phone call is done to ask if the invitation was received and reminding them that they should certainly attend. Then there is this whole category of "personal invite" which is more personal than the "personal invite" post-it stuck on what was already a personal invitation. This is to show that the invited person is not just very very very special. But very very very very very special. So armed with a blouse piece, shirt-bit and teeny-weeny sized pot of kungumam, the parents of the bride rent a call-taxi and go on an inviting spree to meet the invitees directly and plead them to come and attend. This extreme personal invite is to guard against people who give statements like "but it was the postman who invited me and I don't know him well enough"
The invitation process reminds one of what happens in the actual marriage. No, I am not referring to the 2-day silk-saree, gold jewellery and padmanabhan samayal extravaganza. This is the one where the bride and groom really do the work of saying the vedic mantras to actually get married. The priest - if he is from a non-vaikanasa agama school - asks the groom to prefix every mantra - that ends with 'swaaha' and ghee being poured into fire - with "idhanna muh-ma". It means "I am not doing this for my sake" (but for your sake! god). Most grooms who did not fall into the conveniently lazy 'maadern' concept of "I yam spiritual but not religious" would have to actually say this phrase N-1000 times in 2 days. They have to say it so many times that the words replay in your dreams for at least a week. At some point the ritual, priest and the groom get so paranoid that the groom is saying "in case you had any doubt god.. this is not for me". to be followed up with "in case you had doubts after the last time i suspected you of having doubts.. please understand that I am not doing this for me" and a few thousand times later says "if after the 6000 times of saying so - in case you had any doubts - this is not for me".
The bride's father is very similar to the groom here. After inviting people so many times, he has to continue inviting them even after they have actually arrived at the wedding. The saaraya baattil groom may have claimed to be "modern" or "progressive" or "broad minded but spiritual" and would claim that he is "not interested in the archaic rituals and superstitions of the religion". They may even say that "as long as the mind is sincere and honest" everything is just awesome. The groom's family are so modern that they may cut budget by reducing 5 priests to just 1 and 10 rituals to just 2. But that does not mean the bride's family should stop inviting people after the marriage has begun. The people who come for Jaanvasam need to be invited again with "vaango! vaango" and when they leave they need to be given a verbal evite-reminder of "please come for muhurtham and reception also".
Like S. Ve. Sekhar prophesizeed before "thalaivar spelling mistake panna kooda thanakku rs 10,000 laabam vara madhiri dhaan pannuvar". The groom's family may be modern enough to let saaraya bottil have a bachelor pary in a bar near the mandapam but they aren't about to forget the age-old ritual of sixty thousand invitations to the same three people, Rs 10,000 for "reception dress" and 50 pounds of gold hanging on the bride's body. You can't cut any of this and file it under the "spiritual but not religious" account by saying "I have a sincere thought in my mind to give you 50 pounds of gold as dowry but I can give only Rs 3" . Doing so would make the groom's family barbaric.
So the same set up of people are invited by the hosts over and over again for the next 2 days. The are invited to the actual wedding hall, to the kitchen, dining room, beeda stall, ice cream stall, thengai room, maangai room, seer varusai room, bathroom, electrical room, until they have been given the vetthalai paaku and sent out. Because these very very special people are the 'kavari maan'. They get offended at the slightest hint of invite-packet drop. They are sure to call and remind next day that "one coffee was not given" or "that man forgot to invite me for the 60th time". The host's family have only one opportunity to get back. That is when an invited person does not show up and does not even do a "vijaarikarthukku" phone call. Then it is payback time.