Alex Mack signed a five-year deal worth $45 million with $28.5 million guaranteed and an $11.5 million signing bonus. The first two year's salaries of $1.75 million and $6.75 million are guaranteed right off the rip. After the first two seasons, the 2018 salary of $8.5 million will guarantee on May 15, 2017. This gives the Falcons flexibility should Mack decide that he either doesn't want to play anymore or he falls off a cliff skill-wise.
Over the entirety of the deal, Mack will never take up more than $10.3 million towards the cap. And even then, that won't happen until the final three years of the deal when the cap should be well over $170 million each season. The Falcons should be able to build around his deal and a projected Matt Ryan extension during those three seasons. Atlanta has more than enough cap flexibility to make this move make sense.
The Real Contract
It's essentially a two-year deal with the team option to continue through the remaining three years. If Mack doesn't show that he can still be the same player that he once was, the Falcons can cut him after the 2nd year for a cap gain of $3 million that year and wipe his $10-plus million from the books in subsequent years. If he does prove that he's worth the deal, having the best center in the NFL on your team protecting the franchise is easily worth $10 million/year.