Yes, there is a cap on how many mails can be sent from 1 person to another in a certain amount of time. Give it a little while, and he can send more mails. Hopefully 5 mails worth of ingredients are enough to last you until tomorrow.

I'm not sure exactly what you're asking on melding, but here's a primer on melding. It includes the location for the Melding quests. If I remember correctly, you generally need a crafting class at level 19 before you can accept the melding quest.