Change the PDF compression settings via the 
icon in the general PDFMAILER settings.
PDF Settings / Compression
Select the compression algorithm via “Image compression” with which the images in your document will be compressed when converting to PDF format.
Use the option “Recalculate to” to define the resolution to be used for the recalculation of the images in your document when converting to PDF.
As a general rule, the image quality will improve with higher resolution, but the generated PDF file will also be “heavier” the higher the resolution.
gotomaxx PDFMAILER embeds all fonts (the subsection of characters used) included in your document in the generated PDF by default. That ensures that the generated PDF documents can be displayed on any system in its original state. Depending on the font used, this may marginally increase the file size of your PDF document. You can deactivate this function via “Embed all fonts used”.
That means, however, that all fonts used in your document must be installed as standard on any system on which the PDF will be viewed to ensure optimal visualisation.
You can ensure that the PDF is generated in compliance with the PDF/A-1b archiving standard by selecting “PDF/A-1b” if you select a custom setting.