postfix only send mail from ubuntu 16.04

i have install postfix on ubuntu 16.04 for send-only mail.
when i send mail nothing happend nor error and  don't send mail.
service status on postfix  is
fatal: bad numerical configuration: mailbox_size_limit = 20M
fatal: bad numerical configuration: mailbox_size_limit = 20M
warning: process /usr/lib/postfix/sbin/local pid 12388 exit status 1
warning: /usr/lib/postfix/sbin/local: bad command startup -- throttling

what is wrong here what should linit be?
Jasmin shahrzadAsked:
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MichelangeloConnect With a Mentor Independent ConsultantCommented:
Please ese 20480000 as value
mailbox_size_limit = 20480000

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Note: 104857600 is 100 (MB) x 1024 (KB) x 1024 (Byte).
After that check postfix status with
tail +50  /var/log/mail.log 

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Michelangelo stated correctly that you need to alter the mailbox_size_limit. However 20480000 bytes is actually  19.5MB so you're half a MB short if you need a 20MB mailbox size limit.


1 Byte = 8 Bit
1 Kilobyte = 1,024 Bytes
1 Megabyte = 1,048,576 Bytes
1 Gigabyte = 1,073,741,824 Bytes
1 Terabyte = 1,099,511,627,776 Bytes

So with that in mind 20MB makes 20,971,520 bytes

Just edit the and you're set.

# less /etc/postfix/
message_size_limit = 20971520

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MichelangeloIndependent ConsultantCommented:
Thank you dfke for pointing that out. I made a little search and have to amend my comment:
104857600 is 100 (MB) x 1024 (KB) x 1024 (Byte) is not true.
20M = 20480000  20 x 1000 x 1024
It seems in recent years International standards define 1000 (and not 1024) as order of magnitude for storage capacities as does Google storage calculator:

Google Storage Calc
Point is, the issue user is having is about the notation: 20M is not accepted by, you need to specify the exact number of kilobytes
The value you put in is of course up to you, be it 20480000 (postfix default value) or  20971520.
MichelangeloIndependent ConsultantCommented:
Issue is about notation used in
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