Postfix message_size_limit

[vpx]

In the Postfix plugin the default value is 51200000 Bytes.

I know it follows the convention of the original documentation.

message_size_limit
(I linked via Wayback Machine as I don't know why the Postfix site is currently offline)

But does anybody know why that is?

I mean it is calculated as 50x1024x1000 = 51200000 Bytes.

Shouldn't it either be 50x1024x1024 = 52.428.800 Bytes or 50x1000x1000 = 50.000.000 Bytes?

I know the diference between KiB and KB, MiB and MB etc. but why is it a mixed case here?

[Patrick M. Hausen]

I read that as 512 x 100.000. One power of two, one power of ten.

[vpx23]

OK, I found the explanation on Wikipedia:

The IBM System 360 and the related disk and tape systems set the byte at 8 bits and documented capacities in decimal units.[38] The early 8-, 5.25- and 3.5-inch floppies gave capacities in multiples of 1024, using "KB" rather than the more accurate "KiB". The later, larger, 8-, 5.25- and 3.5-inch floppies gave capacities in a hybrid notation, i.e., multiples of 1024,000, using "KB" = 1024 B and "MB" = 1024,000 B. Early 5.25-inch disks used decimal[dubious – discuss] even though they used 128-byte and 256-byte sectors.[39] Hard disks used mostly 256-byte and then 512-byte before 4096-byte blocks became standard.[40]

Source

Being an IBM product it makes sense that this hybrid notation was used in Postfix.

[JeanMitchell]

Yeah, this confused me the first time I noticed it too. It's basically one of those old "computer storage math" leftovers where vendors mixed binary and decimal calculations together. Postfix inherited that convention years ago, so 51,200,000 bytes ended up being treated as the practical "50 MB" default even though it's technically neither pure MiB nor pure MB.

Not the cleanest convention, but pretty common in older software and storage-related tooling.