One has 875 members at present, the other 777.It makes relatively little difference how the message was posted.
What matters is how many of your members are on Individual messages: one posted message becomes a burden of up to 875 outbound messages, or 777 in the other group. For most groups the outbound burden is a significant multiple of the number of posted messages.
To my way of thinking, my email “load” is on the FatCow server (POPOnly the messages sent to you are a burden on FatCow (well, plus the messages sent to any other group members that use that service).
and I fail to see how that is in any manner a “burden” on Groups.ioExactly as you described.
In every email transmission there's both a sender and a receiver, and each uses computational and communications resources to process the email transmission. In the case of each outbound message Groups.io is the transmitting part of all of those transactions, where the reception part is distributed among the members' various email services.
Additionally, I have no idea how those using POP accounts and thoseOnce the message has been transmitted to the member's service it no longer matters to Groups.io. How the member accesses the message is purely between the member and his/her email service.
On the other hand, members that choose to read the message directly from the group's Messages section on Groups.io do incur some amount of processing and transmission cost, again on both Groups.io's web server and at the member's internet service. I don't know how the cost of this web transaction compares to an email transmission, but I imagine it is comparable, or possibly greater.
All those hard-working electrons (and photons).