Having problem sending bulk email

If i want to start bulk email campaign then, how much email id i can add in a segment, after starting a campaign it stops after a sudden period of time, If i would like to start a smooth campaign then how it is possible?

If i want to start bulk email campaign then, how much email id i can add in a segment, after starting a campaign it stops after a sudden period of time, If i would like to start a smooth campaign then how it is possible?