E-Mails in SENT Folder not older than 7 days

[Krazy_Peanut]

Hi guys,
for some reason my iPhone deletes messages inside the SENT folder (not trash!) which are older than 7 days. I cant find settings for that. Does anyone know how to change this?

 

[BrianBaughn]

Who is your email provider? Does the webmail portal for the account show the same? Are there any rules/filters set at the webmail portal? Are the missing emails in the Archive/All Mail folder?

Is the account accessed via an email client application on a computer? Are there any email rules set up on that application?

 

[Krazy_Peanut]

Who is your email provider? Does the webmail portal for the account show the same? Are there any rules/filters set at the webmail portal? Are the missing emails in the Archive/All Mail folder?

Is the account accessed via an email client application on a computer? Are there any email rules set up on that application?

It's United Domains (German one) and I am using Thunderbrid on the PC. I have checked the settings on Thunderbrid on the PC and its set that it doesnt delete any messages. It must be something on the iPhone but I just cant find any settings other than the ones that say what to do with the DELETED messages. It is only inside the Sent folder.