Nothing about the program itself is subscription based. All of the normal features of an email client (that you would also find in Thunderbird) are available for free. You only need to pay if you want to use their services like Send later, read receipts or link tracking, because these requires backend servers and actually costs the money.
Great, a subscription based mail program. Because that’s clearly what people want and need, paying rent for the software on their machines.
Nothing about the program itself is subscription based. All of the normal features of an email client (that you would also find in Thunderbird) are available for free. You only need to pay if you want to use their services like Send later, read receipts or link tracking, because these requires backend servers and actually costs the money.