Ever more people hover over links provided on emails to see if the destination address looks safe.
When a link is inserted in a Constant Contact email campaign it appears as a exceedingly long and scary address in a Constant Contact server, rather that the simple address that the link intends to take the user to. If the user is naive enough or fearless enough to click anyway, the link works. But some of the recipients may become suspicious of the email sender.
Here is an example: The link to the home page of pwol.ca (https://pwol.ca) Appears on the email as directing the user to the following address: