Email signature compatibility guides
Focused explanations of common HTML signature failures. Important guides link back to the checker so you can test the exact HTML you are working with.
Outlook Classic
Outlook email signature checkerUnderstand the Classic Outlook compatibility model and check existing HTML.Line-height problems in Classic OutlookMicrosoft-backed guidance for unitless values and line-height on span elements.Margin and padding in Classic OutlookMicrosoft-backed guidance for spacing in compatibility-sensitive signature layouts.Background images in Classic OutlookMicrosoft-backed guidance for CSS backgrounds and Outlook-specific handling.Why flexbox is risky in Classic Outlook signaturesA conservative layout heuristic for Word-based rendering environments.SVG images in Outlook signaturesWhy raster fallbacks are often safer for important logos and icons.
Gmail and image HTML
Gmail signature too longGoogle’s documented 10,000-character signature limit and how to reduce markup.Base64 images in email signaturesWhy data-URI images can be fragile across signature workflows.Relative image URLs in email signaturesWhy web-page-relative asset paths stop being dependable inside email clients.
Want the coverage contract instead?
The Rules Library shows every current SigLint check, its severity and evidence level. The methodology explains what a finding does—and does not—prove.