November 29, 2020

Configure max fetching size of e-mails in OTRS / Znuny / OTOBO

In Znuny / OTRS / OTOBO there are some good defaults defined. E.g. for fetching e-mails a typical default of 16MB is defined. This could be in some cases far too low. You want now to change the maximum size of the e-mails in OTRS / Znuny / OTOBO?

You are unsure if the e-mail size is your issue?

In this case check the error logs with How to debug e-mail errors in OTRS?

Configure max e-mail size for receiving

In SysConfig you can find under the SubGroup Core::PostMaster the configuration PostMasterMaxEmailSize. Here you define the total size of your e-mail.

One common mistake here is to assume the attachment size only. Lets say you have a attachment of 20MB your real message size can go up 40% more due to the Base64 encoding of binary data in e-mails. So a good rule of thumb is to add 50% more on PostMasterMaxEmailSize as your real message size could be.

The real possible message size is limited by your E-Mail provider or your Mail-Server Administrator. They can tell you what the biggest allowed size of E-Mails is allowed. You should add on top of this size the above named overhead of 50%. E.g. some examples

  • GoDaddy: 30MB
    => you shall define at least 45MB (see below why)
  • IONOS: 25MB (or bigger depending on your plan)
    => you shall define at least 37.5MB (see below why)

As an example you want to allow 25MB of total e-mail size. The Base64 encoding would increase it to about 34MB (about 35% more). A good standard would be to set in this case the limit to 25+25*50%=37.5MB or rounded up to 40MB.
Means PostMasterMaxEmailSize=40960 since the value is entered in KByte size.

Common errors on wrong e-mail size

Can’t fetch email from. Email too big

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